BMW M350 xDrive vs Audi S5, AMG C43, M340i, M3 and the Fast EVs: Which Fast Saloon Makes Sense in 2026?

Images: BMW Group

For the best part of a decade, the M340i has been the answer to a very particular question: what do you buy if you want a properly quick saloon that doesn't shout about it? It was fast, comfortable, quietly well made, and it took modifications well. Now BMW has replaced it. The new G50 3 Series brings the M350 xDrive, and the M350 has rivals that are better than ever: Audi's new S5 Saloon, Mercedes-AMG's C 43, BMW's own M3 one step up, and a set of fast electric saloons that didn't exist when the M340i arrived.

This guide is for the buyer who reads the spec sheet before the brochure. We compare how each car makes its performance, what it weighs, how it puts its power down, and what that means on a wet B-road in February. Then we finish with what interests us most: how we'd spec an M350, and how we'd modify one without spoiling what BMW got right.

If you want the full G50 range, specifications and on-sale dates, our BMW 3 Series G50 guide covers it in detail. We won't repeat those tables here.

The contenders, and why we chose them

A fast saloon in this class has to do two jobs. It has to be an easy, quiet, comfortable car for 90% of the week, and a genuinely rewarding one for the other 10%. Every car here manages both. They just get there differently.

Sources: BMW UK PressClub (M350), BMW UK technical data (M340i, M3), Audi UK (S5), Mercedes-Benz UK (C 43), Polestar UK.

Who isn't here. Mercedes-AMG doesn't currently list a C 53 saloon in the UK, so it isn't in this comparison. The CLE 53 is a coupé, which puts it in a different conversation. And while plenty of people search for the Audi S4, the S5 Saloon is now the car Audi sells in this slot.

Engines: three ways to build a fast saloon

This is where the cars differ most, and where it's worth slowing down.

BMW M350: the straight-six, refined again

The M350 uses BMW's 3.0-litre inline six with 48-volt mild-hybrid assistance. BMW's technical data gives the full picture:

Source: BMW technical specifications, M350 xDrive, 09/2026.

Why this matters: the electric motor adds only 18 hp, but it adds 200 Nm of torque. That torque arrives instantly, exactly where a turbocharged engine is weakest: in the moment before the turbo spools. The engine already makes its full 540 Nm from under 2,000 rpm. The motor fills the gap before that. In practice, you get a car that responds the instant you touch the throttle, without needing to be in a low gear or high revs. That's the difference between a car that feels quick and one that feels effortless.

The long stroke tells the same story. Engines with a stroke longer than their bore tend to favour torque over top-end revs. Paired with an eight-speed gearbox that keeps the engine in its broad torque band, it suits real roads more than track days. That is exactly what this car is for.

Why a mild hybrid, and not a plug-in?

It's a fair question from anyone who follows the technology. A plug-in hybrid carries a large battery and a powerful motor so it can drive on electricity alone. That brings weight, and on a performance saloon, weight is the enemy. A mild hybrid takes a different route. BMW's data lists a 48-volt battery of 19.2 Ah alongside the usual 12-volt battery (BMW technical data). At 48 volts that's a little under 1 kWh: tiny next to an EV's battery, but plenty to store braking energy and release it as a burst of torque.

The engineering logic is that you don't need much stored energy to transform how a car responds. You just need it to be available at the right moment. A 48-volt system can deliver far more current than a 12-volt one, which is what allows a motor with 200 Nm of torque without the size and weight of a high-voltage system. For a buyer who wants the response of electrification with the weight and character of a petrol six, that's a sensible compromise.

Turbo lag, and why it has almost gone

Every turbocharged engine waits a moment for exhaust gas to spin the turbine before full boost arrives. BMW's answer on the M350 is to give the engine a broad torque band (540 Nm from 1,980 rpm) and let the electric motor cover the moment before that. The goal is a car that responds the instant you ask.

BMW M340i: the same idea, one step earlier

It's easy to forget that the outgoing M340i already used 48-volt assistance. BMW UK's technical data lists it at 288 kW (392 hp) system output and 540 Nm, made up of 280 kW (381 hp) from the engine plus 9 kW (12 hp) from the 48-volt motor (BMW UK).

So the M350 isn't a revolution. It's a careful development of a familiar recipe: more power from the engine itself, a stronger electric motor, and a new car around them. If you've driven a recent M340i, you'll recognise the character. You'll just find more of it.

Audi S5 Saloon: big output, quattro first

Audi UK lists the S5 Saloon TFSI quattro at 367 PS and 550 Nm, with 0–62 mph in 4.5 seconds (Audi UK). Its standard quattro with sport differential is the interesting part, and we come back to it in the all-wheel-drive section. On paper, it gives up power to the M350 but sits close on torque.

Mercedes-AMG C 43: the four-cylinder argument

Mercedes takes the most radical route. The C 43 uses a 1,991 cc four-cylinder with mild-hybrid assistance, 500 Nm of torque, and a nine-speed AMG SPEEDSHIFT MCT gearbox (Mercedes-Benz UK). Mercedes UK's current output figures differ between versions, so we aren't quoting a single power figure here. Check the version you're looking at.

Why it matters: a small, highly boosted four-cylinder can match a six on output. What it can't match is the six's natural smoothness and sound, which is why the C 43 divides opinion among enthusiasts. Some drivers love its eagerness. Others miss the six. This is worth a back-to-back test drive, not a spec-sheet decision.

Torque and output side by side

BMW quotes "hp" in metric horsepower, which is the same unit as Audi's PS. We've left gaps where a maker's UK page didn't give a figure we could confirm, rather than fill them from elsewhere.

Weight, aerodynamics and why they matter

Power figures sell cars, but weight shapes how a car feels: how quickly it changes direction, how hard the brakes work, and how long the tyres last.

BMW gives the M350 two weights: 1,860 kg DIN and 1,935 kg EU (BMW technical data). The difference isn't a contradiction. The EU figure includes a 90% full tank and a 75 kg driver, as BMW UK explains in its technical notes. Use the EU figure when comparing cars. It's closer to how you'll actually drive one.

Makers measure kerb weight in slightly different ways, so treat the per-tonne figures as a guide. The point is clear, though. The M350 carries similar performance per tonne to one of the quickest electric saloons while weighing roughly 170–250 kg less.

Aerodynamics is the other half of efficiency at speed. BMW quotes the M350's drag as Cd 0.28 with a frontal area of 2.29 m². Multiply them and you get 0.64 m², the "drag area" that matters for fuel use at motorway speeds. The car is 4,765 mm long, 1,850 mm wide and 1,455 mm tall, on a 2,860 mm wheelbase (BMW technical data). BMW also says the combustion models keep near-perfect weight distribution (BMW UK PressClub), which matters more than any single power figure on a twisting road.

Design and presence

The M350 is visually distinct from the rest of the G50 range. It gets M Yellow Lights (active at night with the low beams), a boot lip spoiler, and four tailpipes at the rear (BMW UK PressClub). The Neue Klasse design itself is cleaner and more reduced than the G20, with the kidney grille and headlights integrated into one horizontal element, flush door handles and a low character line.

For a buyer who prefers factory-look modifications, that's good news. A clean, reduced design takes subtle changes well, such as a slightly lower stance, wheels that fill the arches, and a touch of carbon. Whether those parts exist yet is a separate question, which we answer at the end.

The rivals take their own approaches. The Audi S5 Saloon's design, by Audi's description, has flared wheel arches, aerodynamically shaped air inlets and an electric tailgate that opens with the rear window, which makes it something closer to a five-door. The M3 is the most overtly aggressive of the group.

Chassis: the quiet engineering story

The headline change on the M350 isn't the engine. It's what holds the wheels.

BMW's technical data lists a double-wishbone front axle in aluminium-steel for the M350, with a five-link rear axle (BMW technical data). A double-wishbone front end controls the wheel's camber more precisely as the suspension moves. That keeps more of the tyre on the road when you're cornering hard, and it separates steering feel from bump control. It's the kind of change you notice in the first few corners, rather than on the spec sheet.

Other details from the same data sheet:

• Brakes: four-piston fixed callipers at the front, single-piston floating callipers at the rear, all ventilated.
• Steering: electrically assisted, with variable sport steering.
• Suspension: adaptive M suspension is part of the M350's standard specification (BMW UK PressClub). BMW also says revised axle settings and stiffer chassis and anti-roll bar mounts improve body control.
• Turning circle: 12.1 m.

Brakes: why the layout matters

Four-piston fixed callipers at the front clamp the disc evenly from both sides, which gives a consistent pedal feel when the brakes are hot. A single-piston floating calliper at the rear is lighter and perfectly adequate, because the rear axle does much less of the work under braking. That combination is typical of a fast road car rather than a track car. If you plan regular track days, that's another point in the M3's favour.

Why the adaptive suspension matters for owners: adaptive dampers change their stiffness continuously as you drive. That's what lets the same car be calm on a motorway and composed on a fast road. It's also why we're careful about suspension modifications on this car. More on that at the end.

Technology inside: M350 vs S5 Saloon

For a buyer who cares about the interface as much as the engine, these two are the most interesting pair.

Sources: BMW UK PressClub, Audi UK. A dash means the maker's UK page we used doesn't mention it, not that the car lacks it.

The two makers take different routes. BMW projects information onto the windscreen so your eyes stay up, while Audi adds screens, including one just for the passenger. BMW also says the M350's optional Motorway Assistant supports hands-free driving on compatible motorways up to the national speed limit, with the driver still paying attention throughout. If you do long motorway miles, that alone is worth trying on a test drive.

Our view: the BMW system is the more forward-looking of the two. The Audi system is more familiar. Both are a generation ahead of the M340i.

Gearboxes: why they shape the character

How a car shifts gears changes how it feels as much as its engine does.

Sources: BMW UK PressClub and BMW UK (BMW), Mercedes-Benz UK (C 43).

Why it matters: a torque converter is very smooth in traffic and at parking speeds, which is where most saloons spend their lives. A clutch-based gearbox like the MCT feels more direct, especially when you're driving hard. Neither approach is wrong. It's another reason to try these cars back to back rather than choose from a table.

All-wheel drive, done three ways

Every car here sends power to all four wheels, but how each decides where to send it is very different.

Sources: BMW technical data (M350), Audi UK (S5), Mercedes-Benz UK (C 43), BMW UK (M3).

Why it matters: in the dry, all-wheel drive mostly helps you leave junctions quickly. In the wet, it changes everything. A system that can move torque towards the outside rear wheel, as Audi's sport differential and BMW's Active M Differential do, helps the car rotate into a corner instead of pushing wide. BMW's approach on the M350 is software-led. And from 2027, BMW's Drift Moment function will be able to send power to the rear wheels only, through a software update. Our G50 guide explains Drift Moment in detail.

Wheels, tyres and the UK winter

The M350's standard tyres are staggered: 245/40 R19 at the front and 255/40 R19 at the rear, with load ratings of 98 Y XL and 100 Y XL (BMW technical data). In plain terms, the rears are slightly wider to carry more of the drive and the car's weight under acceleration. The "Y" means the tyre is rated for very high speeds, and "XL" (extra load) means a reinforced construction for a heavier car.

Three practical points follow:

1. Rotation: with different sizes front and rear, you can't swap tyres between axles to even out wear. Budget for rear tyres wearing at their own rate.
2. Winter tyres: if you fit winter or all-season tyres, you'll need the same staggered pattern, or a squared setup your tyre supplier confirms for the car.
3. Wheels and spacers: any change in wheel or spacer size has to respect two different widths and offsets, front and rear. That's one reason we're careful about M350 fitment advice until we've measured cars ourselves.

The 20-inch option looks sharper, and many buyers will choose it. Bear in mind that a lower-profile tyre protects the rim less on potholed roads and transmits more of the road into the cabin, even with adaptive dampers.

Practicality: living with it every day

These are family saloons first. The M350 gives you a 450-litre boot, five seats, 40:20:40 split-folding rear seats and a 59-litre fuel tank. It can tow a braked trailer of up to 1,800 kg (BMW technical data). The M3 Saloon offers 480 litres (BMW UK).

For the tech-minded buyer, the cabin may be the bigger change. Every G50 comes with BMW Panoramic iDrive and BMW Operating System X. That means the Panoramic Vision display across the base of the windscreen, a 17.9-inch central display, and a voice assistant built on large-language-model technology (BMW UK PressClub). The M350 also adds a Harman Kardon surround sound system and three-zone climate control as standard. If you've lived with the G20's iDrive, this is a generation ahead, and it's a stronger reason to change car than the extra horsepower.

Touring buyers: m340i touring is one of the most searched terms in this space. We'll cover the G50 Touring once BMW UK confirms its details.

Efficiency and running

Fast saloons are rarely bought for economy, but the figures show how far the technology has moved.

BMW describes the M350's figures as provisional. The useful comparison is with the M3: the M350 delivers much of its everyday pace with noticeably lower consumption. With a 59-litre tank, that's a real gain on long trips.

Keep your M340i or move to the M350?

This is the question we're asked most, and the honest answer is that it depends on why you bought the car in the first place.

What the M350 adds: more power and torque (443 hp and 580 Nm against 392 hp and 540 Nm), a double-wishbone front axle, standard adaptive M suspension, a new cabin and software platform, and Drift Moment from 2027.

What the M340i keeps: a proven B58 engine and a huge range of tested aftermarket parts. Exhaust systems, intakes, springs, spacers and carbon parts for the G20 are all established. For the M350, almost nothing exists yet.

The M340i is still listed by BMW UK, so a well-specified used or nearly new example remains a sensible choice. For owners who stay, we cover the parts we'd fit at the end of this guide.

Software, updates and the early-adopter question

The G50 3 Series uses BMW's Neue Klasse electronics. BMW's Heart of Joy and BMW Operating System X arrive across the range, and features can be added after delivery. Drift Moment is the clearest example: BMW says it will become available during 2027, including on cars already delivered, through a software update (BMW UK PressClub).

For a buyer who likes new technology, this cuts both ways.

The upside: your car can get better after you buy it. Features, interface improvements and driving functions can arrive over the air, as they do on a phone.

The trade-offs: - First-year cars often get software refinements in their early months. That's normal for a new platform, but it's worth knowing if you order at launch. - Aftermarket parts take time. Brands need production cars to design, test-fit and prove parts. That's why the M350 list at the end of this guide is short. - Electronics affect modifications. On a car this integrated, it's sensible to treat anything that touches suspension or exhaust valves as something to discuss before fitting, not after.

Source: BMW UK PressClub, 30 September 2026.

The fast EV question, honestly

Many of you will have driven a fast electric saloon by now, and the acceleration is genuinely remarkable. Polestar UK lists the Polestar 2 Long Range Dual motor with Performance Pack at 350 kW (476 hp) and 740 Nm, with 0–60 mph in 4.0 seconds. Note that's 0–60, not 0–62 (Polestar UK). The Tesla Model 3 Performance is the other obvious name, with dual-motor all-wheel drive. We couldn't confirm its current UK figures from Tesla, so we're not quoting them here.

BMW's own electric 3 Series, the i3 50 xDrive, gives 469 hp and 645 Nm, 0–62 mph in 4.7 seconds and charging at up to 400 kW, with first UK deliveries this autumn (BMW UK PressClub).

So why would a technically minded buyer choose the petrol car? Three honest reasons:

1. Weight. As the table above shows, the M350 is roughly 170–250 kg lighter than the Polestar. You feel that in every direction change, and in how hard the tyres and brakes work.
2. Sound and engagement. A straight-six that makes its peak power between 5,600 and 6,500 rpm is a different experience from silent, instant torque. Neither is better. They're different.
3. Modifying. You can change how a petrol car sounds, sits and looks with established, reversible parts. With fast EVs, the options are much narrower.

And the honest reason to go electric: if most of your driving is local, you can charge at home, and you value quiet speed over sound, a fast EV is hard to argue with. Drive both.

The stretch: G80 M3 Competition

If the budget allows, the M3 Competition M xDrive is a different class of car. BMW UK lists 390 kW (530 hp), 650 Nm and 0–62 mph in 3.5 seconds. The engine is a high-performance M TwinPower six, with M xDrive, an Active M Differential and an eight-speed M Steptronic with Drivelogic (BMW UK).

The M3's options also show what separates it from the M350. BMW UK lists an M Carbon roof to lower the centre of gravity, optional M Carbon bucket seats and an M Carbon Exterior Package (BMW UK). These are the details of a car designed to be driven hard, rather than a fast car designed for the everyday.

Is it worth it? If you'll use the extra performance (a track day, or very quick road driving), yes. The M3 is built for repeated hard use in a way the M350 isn't meant to be. If you won't, the M350 delivers most of the experience with more comfort and less intensity. Its standard 19-inch wheels and adaptive suspension point to a car tuned for real roads. That's the M340i vs M3 question owners have argued over for years, and the answer hasn't changed: buy the car for the driving you actually do.

A test-drive checklist

Spec sheets only get you so far. When you book test drives, here's what we'd try in each car.

Drive the M350 on the wheel size you plan to order. The difference between 19s and 20s on UK roads is real.

Which one suits you?

Specifications only tell part of the story. Here's how we'd match these cars to the people who buy them.

You drive 20,000 miles a year, mostly on motorways, and want one car to do it all. The M350. It has a very refined powertrain, adaptive dampers as standard, and the driver-assistance technology to make long trips easier. Choose 19-inch wheels.

You live somewhere wet, rural and hilly. Look hard at the Audi S5 Saloon. Its standard quattro with sport differential is designed for exactly those roads. The M350's xDrive is very capable too. Drive both on a damp day if you can.

You want something that feels different from the BMW default. The Mercedes-AMG C 43. Its high-revving four-cylinder and clutch-based gearbox give it a character of its own.

You already own an M340i and love it. Keep it. Spend the difference on a Milltek valved system, a careful drop and a few carbon details, and you'll have a car that feels new, with years of proven parts behind it.

You want the ultimate, and you'll use it. The M3 Competition.

You charge at home and most trips are local. Drive a fast EV before you decide. Its instant, silent pace is genuinely compelling. Just be honest with yourself about weight, sound, and how much you want to personalise the car.

Reading the spec sheets: a short glossary

Makers publish figures in slightly different ways, and it's easy to compare the wrong numbers. Here's what to watch for.

Sources: BMW UK technical notes and M3 page footnotes, BMW technical data, Polestar UK, Audi UK.

Our verdict

• Best all-rounder: the BMW M350 xDrive. A refined six-cylinder with a 48-volt motor, a reworked front axle, a strong technology package, and lighter than the fast EVs we looked at.
• Best for confident wet-weather driving: the Audi S5 Saloon, thanks to its standard quattro with sport differential.
• Most distinctive: the Mercedes-AMG C 43. Drive it before you decide, because its four-cylinder approach divides opinion.
• Best if you already own one: keep the M340i and modify it. The parts are ready today.
• Best for the fastest drivers: the M3 Competition.

How we'd spec and modify one

This is the section our customers ask us about most. Our approach to the M350 is simple: start with BMW's best specification, then make careful, factory-look, reversible changes, and only with parts that actually exist.

How we'd spec it

• Wheels: BMW fits 19-inch wheels as standard, with 20-inch optional (BMW UK PressClub). BMW's data lists the standard tyres as 245/40 R19 front and 255/40 R19 rear, on 8.5J front and 9J rear rims (BMW technical data). That staggered setup is deliberate: wider rear tyres for traction and balance. For a car used every day, we'd keep the 19s. The taller sidewall protects the wheels and suits the adaptive suspension.
• Suspension: the adaptive M suspension is standard on the M350, so there's nothing to add here.
• Trim: M Sport Pro features such as Iconic Glow and sun protection glass are worth having if you keep cars for a while. The M350 adds Harman Kardon sound and three-zone climate as standard.

Why factory-look?

There's a good reason we steer customers towards subtle changes on cars like these. The M350, M340i and S5 are bought partly for their discretion: fast cars that don't draw attention. A modification that respects that, such as a slightly lower stance, wheels that sit flush with the arches, a carbon mirror cap or a valved exhaust that's quiet when you want it to be, makes the car more yours without making it less usable. They are also the changes that are easiest to undo, which matters on a car you might sell or return in three years.

Standard equipment worth knowing

BMW positions the M350 at the top of the petrol G50 range. Beyond the M Sport Pro features, BMW UK lists Harman Kardon surround sound, adaptive M suspension and three-zone automatic climate control as standard. The M Sport Pro features include electrically adjustable M Sport seats, red M Sport brakes, an M steering wheel, M seat belts, black exterior mirror caps, BMW Iconic Glow and sun protection glass (BMW UK PressClub). Full BMW Individual paint personalisation follows from 2027. If a particular colour matters to you, that's worth knowing before you order.

What exists for the M350 today

That's not a gap we'll paper over. A new car needs time for parts to be designed, test-fitted and proven. We would rather tell you there's nothing yet than sell you something unproven.

Our M350 approach today: keep the factory ride and stance, and if you want a flusher wheel position, talk to us about spacers. Bimecc's listing includes its own advice on possible arch contact, and that's worth reading before you choose a size.

Already in an M340i? Here's what we'd fit

For G20 owners, the choice is wide and proven. Kept subtle and factory-look, this is how we'd do it.

Sound, and keeping it civil. The Milltek exhaust system for the M340i xDrive (OPF/GPF models), with Milltek's Active Valve Control plug-and-play system, lets you choose when the car is quiet and when it isn't. That matters on a car you use every day. To finish the rear, TREVORA ID-01 quad exhaust tips.

A careful drop. Eibach Pro-Kit lowering springs give a modest, factory-look drop. For flush wheels, the Bimecc G20 spacers: check the size on the page.

Subtle carbon. - TREVORA pre-preg carbon PR-1 rear spoiler - FORM pre-preg carbon mirror covers - For LCI cars, the FORM pre-preg carbon front grille - For pre-LCI cars, the ADRO carbon front splitter and carbon rear diffuser. The white M340i in our photos wears an ADRO front splitter.

Intake. The Eventuri carbon intake for the B58 is as much about what you see under the bonnet as what you hear.

What we'll be watching as cars arrive

The first UK M350s are due in January 2027. When we have cars in the workshop, these are the questions we'll answer first:

• Real-world weights of UK-spec cars on both wheel sizes.
• Wheel and tyre fitment: offsets, clearances and what fills the arches without rubbing.
• Suspension behaviour: how the adaptive M suspension responds to any change in ride height, and what that means for owners who want a lower stance.
• Exhaust: how the factory system is built, and what a valved aftermarket system could sensibly do on a mild-hybrid car.
• Carbon styling: which factory parts can be replaced cleanly, and which can't.

Until then, we're not guessing. That's the most useful thing a parts specialist can say about a car this new.

Our principles, whichever car you choose

1. Bolt-on and reversible. Every part above can be removed again. Keep the original parts in the loft.
2. Factory look first. If someone who doesn't know cars can't tell what's changed, you've probably got it right.
3. Talk to us before you change the suspension on a car with adaptive dampers. We'll tell you what we know, and what we don't yet.
4. One change at a time. Fit a part and drive it for a week before you decide on the next.

Browse our G20 3 Series range, or keep an eye on the M350 collection as parts arrive.