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

Most M340i owners we talk to bought the car for the same reason. It's quick enough to be faintly ridiculous, quiet enough to forget about, and it never asked for anything in return. So when BMW announced the M350 xDrive, the question that mattered was whether they'd spoiled the recipe, with speed a long way down the list.

On BMW's figures, they haven't. The B58 straight-six is still there, so are xDrive and the eight-speed automatic. What's changed is how hard the engine works and what has been done around it. We'll go through what's different from the M340i you know, how it lines up against the Audi S5 Saloon, the Mercedes-AMG C 43 and the M3 above it, and where a fast electric saloon fits in. Then we finish with the few things we'd do to an M350 or an M340i. If you want the whole G50 range, dates and trims, our BMW 3 Series G50 guide covers it.

M350 vs M340i: what BMW has changed in the B58

The M340i launched in 2019 with 374 hp and 500 Nm. BMW puts the M350 at 69 hp and 80 Nm more.

Look at the M350's engine on its own: 426 hp and 540 Nm, with that torque available from 1,980 rpm all the way to 5,400 rpm. The engine alone now makes more torque than the whole M340i launched with. A 13 kW electric motor, good for 200 Nm itself, takes the pair to 580 Nm. If you've lived with a G20 you know how much 500 Nm feels like, and this is a good deal more of it, spread over a very wide band of revs.

Bore and stroke are 82.0 by 94.6 mm, a long-stroke layout that favours mid-range pull, and the compression ratio is 11.0:1, which is high for a turbo engine. It's built for strength low down rather than a screaming top end. BMW gives peak power as a plateau between 5,600 and 6,500 rpm, which we'd read as a car that wants you to use the middle of the rev range.

The electric side is small, a 19.2 Ah battery at 48 volts, a little under 1 kWh. We think BMW has made the right call. A plug-in hybrid would add a large battery and a lot of weight to a car that is already heavier than it was, and a small motor and battery that add 200 Nm is a sensible trade. As we read it, the motor's job is to cover the moment before the turbos have built boost, the one part of a turbo engine's behaviour most owners notice. For an M340i owner, this is the engine you know with a good deal more of it.

M350 vs Audi S5, AMG C 43 and M3: power and weight

The Audi S5 Saloon is the obvious comparison, because it's a fast, grown-up four-door with all-wheel drive from a maker whose customers also read spec sheets. The M3 sits one step above, and everything below it is an argument about character.

The M350 has about 75 more horsepower. What's more telling is torque, where the Audi is only 30 Nm behind (Audi UK). On paper the M350 is the faster car and the S5 the closer match on torque, and the 0.4 seconds between them is the sort of difference you notice on a slip road and forget by the next roundabout.

The Mercedes-AMG C 43 takes the opposite route. It's a 1,991 cc four-cylinder with mild-hybrid assistance, 500 Nm and a nine-speed gearbox that uses a multi-plate clutch instead of a torque converter (Mercedes-Benz UK). We'd pick the six. A small turbo four can match a big engine's output, but it can't match the sound or the smoothness, and those are exactly what a buyer in this part of the market is paying for. If you prefer a car that feels different to the BMW default, drive it. There's no C 53 saloon on Mercedes UK's list, and the CLE 53 is a coupé, so the C 43 is the Mercedes that belongs here.

The M3 Competition is simply a faster car: 530 hp, 650 Nm and 3.5 seconds (BMW UK). Anyone who wants repeated hard use should buy the M3.

Weight is where the M350 asks for a little forgiveness. BMW quotes 1,860 kg to DIN and 1,935 kg to the EU standard, which includes a 90% full tank and a 75 kg driver. On the EU figure that's 190 kg more than the 1,745 kg the M340i quoted at launch, and we'd expect it to show in tyre wear and brake life. It's also a longer car, at 4,765 mm on a 2,860 mm wheelbase, with a drag coefficient of 0.28 on a frontal area of 2.29 m², and BMW says the combustion cars keep near-perfect weight distribution.

Suspension and brakes

The M340i already had adaptive dampers, and the M350 has them as standard, so they're not what's new. What BMW says it has changed is the axle settings and the stiffness of the chassis and anti-roll bar mounts, all aimed at keeping the body flatter. The steering is electrically assisted with variable sport steering, and the turning circle is 12.1 metres.

That matters to anyone who modifies cars, because it changes the job a lowering spring has to do. On a G20, a modest drop works with the factory dampers and the geometry you know. On the M350, with different mounts and a heavier car, a G20 spring may not behave the same way. We have no M350 lowering springs yet. Our G50 guide goes into the geometry changes in more detail.

The brakes are four-piston fixed callipers at the front and single-piston floating callipers at the rear, all on ventilated discs, with red M Sport brakes as part of the M Sport Pro features.

All-wheel drive

Every car in this comparison drives all four wheels, and they go about it differently. The M350's xDrive works with the stability control and BMW's Performance Control. The S5 has quattro with a sport differential as standard, which moves torque between the rear wheels to help the car turn in. The M3 uses M xDrive with an Active M Differential, and the C 43 has permanent 4MATIC.

In the dry, any of them leaves a junction well. In a wet British February, the differences matter more. A system that can push torque to the outside rear wheel helps the car rotate in a corner instead of washing wide, and on paper that's exactly what the Audi's sport differential is for. The M350 gets its own extra. Drift Moment, which sends drive to the rear wheels only, arrives during 2027 as a software update, including for cars already delivered. It's a lovely idea, and it's the sort of feature to save for a private road or a track day.

Inside, and the software

This is where an M340i owner will feel the biggest jump, and we think it's a stronger reason to change car than the extra 69 horsepower. The M350 has BMW's Panoramic Vision display across the base of the windscreen, a 17.9-inch central screen, an optional 3D head-up display and a voice assistant built on large-language-model technology. Harman Kardon sound and Driving Assistant Plus are standard, and BMW lists an optional Motorway Assistant for hands-free driving on compatible motorways up to the national speed limit, with the driver still watching the road.

Audi has gone the other way. The S5 Saloon has an 11.9-inch curved virtual cockpit, a 14.5-inch panoramic MMI screen, Bang & Olufsen 3D sound as standard, and an optional passenger display (Audi UK). BMW puts information in your eyeline on the glass, while Audi adds more screens. We prefer BMW's idea because it keeps your eyes up, but we'd want a long motorway drive in each before saying so with any force.

The software is the other side of it. If you like new technology you'll like a car that improves after you've bought it, and BMW has been clear that features will arrive that way, Drift Moment included. The catch is that you're buying into a new platform at the start of its life. Production begins at Dingolfing in November 2026 and UK cars arrive in January 2027, and first-year cars on a new electronic architecture often get a round of updates in their first months. That's no reason to avoid one, but it's fair to expect some fine-tuning, and to talk through anything that touches the suspension or exhaust valves before it's fitted.

Looks, wheels and everyday use

The M350 is the only car in the G50 range with M Yellow Lights, which are active at night with the low beams, plus a boot lip spoiler and four tailpipes. The face is cleaner and more reduced than the G20's, with the kidney grille and headlights joined in one horizontal element. We think a reduced shape suits modified parts, because there's less for them to argue with. A slightly lower stance, wheels that fill the arches and a little carbon can all sit quietly on a design like this. The Audi, for comparison, has flared arches and an electric tailgate that opens with the rear window, so it behaves more like a five-door.

The standard wheels are 19-inch, staggered, with 245/40 R19 tyres at the front and 255/40 R19 at the rear on 8.5J and 9J rims, and 20-inch wheels are optional. We'd keep the 19s. Taller sidewalls look after your wheels on potholed roads and sit better with a car that is meant to ride well, and we expect the difference between 19s and 20s on a UK B-road to be obvious. Because the sizes differ front to rear, you can't rotate tyres across the car, and winter tyres will need the same staggered pattern. If you move to different wheels or spacers, the front and rear widths and offsets both have to be right.

It's still a family saloon. The boot is 450 litres (the M3 offers 480), the fuel tank holds 59 litres, and the M350 can tow a braked trailer of up to 1,800 kg. On economy, BMW's provisional WLTP figures show where it sits:

On those numbers the M350 is a good deal lighter on fuel than the M3. WLTP figures are good for comparing cars with each other, and less good as a promise about your own commute.

What about a fast electric saloon?

Many of you will have driven one by now, and the way they accelerate is hard to argue with. Polestar UK lists the Polestar 2 Long Range Dual motor with Performance Pack at 350 kW (476 hp) and 740 Nm, with 0 to 60 mph in 4.0 seconds, and a weight of 2,105 to 2,182 kg (Polestar UK). BMW's own electric 3 Series is the same idea with a battery: 469 hp, 645 Nm and up to 400 kW charging.

Put the Polestar next to the M350 and the output per tonne is close, at about 218 to 226 hp against about 229 for the BMW on its 1,935 kg EU weight. The difference is that the M350 carries it in a body 170 to 250 kg lighter, which should show in how the car changes direction and in how hard the tyres and brakes have to work. A straight-six also gives you something an EV can't, which is the sound, and a petrol car has far more established, reversible ways to change how it sits and looks.

There's a fair case for electric too. If you charge at home, most of your miles are local and you value quiet speed over noise, a fast EV is hard to beat. We'd simply drive both before deciding.

Should you keep your M340i or buy an M350?

If you're happy with your M340i, keep it. It's a proven car. The B58 and the chassis around it are well understood, there's a wide range of tested parts, and the fitment questions have long since been answered. A well-sorted M340i is still a seriously quick car, and the M350's extra 69 hp over the 374 hp it launched with isn't a reason to leave it.

The reasons to move are the cabin and the technology. If you buy cars early, like the idea of one that gets better through software and want the newest BMW saloon short of an M3, the M350 is worth waiting for, provided you can live without modifications for a while. If you'd rather start modifying straight away, the M340i has years of parts behind it and the M350 has almost none.

If you want much more performance than either, the M3 Competition is the answer. BMW UK lists a carbon roof, carbon bucket seats and an M Carbon Exterior Package among its options, which is the sort of kit that says what the car is for (BMW UK). It's also the car for anyone who plans real track use.

How we'd spec an M340i or an M350

The M350. Keep the 19-inch wheels. BMW says full BMW Individual paint personalisation follows from 2027, so if colour matters, wait for it.

For modifying one, we'd sooner be straight about where things stand. We have no lowering springs, carbon styling or valved Milltek exhaust for the M350 yet, and a new car needs time for parts to be designed, test-fitted and proven. What we do list is Bimecc G50 spacers, so check the size on the page and read Bimecc's own advice on possible arch contact before choosing. Wheels are in the M350 collection, and you should ask us about fitment for your car before ordering. When UK cars reach the workshop in January we'll start with real weights, wheel and tyre fitment, and how the suspension reacts to any change in ride height.

The M340i. If you're keeping yours, three things would be our first choices.

The first is sound. The Milltek exhaust for the M340i xDrive (OPF/GPF models) with Milltek's Active Valve Control plug-and-play system lets you decide when the car is quiet and when it isn't, which matters on a car you use every day.

The second is stance. The Eibach Pro-Kit lowering springs give a modest, factory-look drop, which is as far as we'd go on a car that already sits well.

The third is a little carbon. The TREVORA pre-preg carbon PR-1 rear spoiler changes the back of the car without changing its character, which is the test we apply to everything.

Everything else for the G20, from exhaust tips and mirror covers to grilles, splitters, diffusers, spacers and intakes, is in our G20 3 Series range. Whichever car you own, we keep to the same few rules. Everything should be bolt-on and reversible, so keep the original parts. Fit one change at a time and live with it for a week. And talk to us before changing the suspension on a car with adaptive dampers, so we can tell you what we know and what we don't yet. We'll add to the M350 collection as parts arrive.

Images: BMW Group (the hero and the red M350 photographs). The white M340i photographs are ours.