At first glance, it looks bad for the new C63 as it’s lost so much. Gone is that glorious 6.2-litre V8, replaced by a 4.0-litre version. Granted, it now has twin turbos and even more power, but is that enough to see off the total aggression of the BMW M3?

The C63 delivers its enormous performance with a certain languid charm. It’s quick, no issue, as that dash to 62mph in just 4.3sec shows – a time identical to that of the M3. But it delivers with a basso profundo growl that rises to a bellow and the sense of theatre is palpable. There’s so much torque to go with the horsepower that it means you can simply churn along without any chance of scaring the horses.

The BMW M3 gives away both power and torque, but the straight-six makes up for it with manic urgency. The noise isn’t so good, more rough and uncouth in this company, but there’s no arguing with the effect. There’s a snap and a snarl to it, and if you let it rev out then it really does deliver with M for Monster.

You can extract every ounce from the BMW by using the adaptable shift patterns on the automatic gearbox. This gives you instant response, on the button shifts, but the effect can be a bit grabby, a bit urgent. The Mercedes-AMG delivers its power with more fluency, simply smoother.

Even the C63’s launch control is a more refined thing that the BMW’s. That emotion continues over into the ride quality, where the Merc cossets and pampers you even as it hurtles along. The BMW has a rougher ride that’s for sure, but of course this translates into incredible cornering ability. It can corner harder, flatter, faster than just about any saloon, certainly more so than the C63. The Merc has tons of lateral grip, but it doesn’t have that focus on the ragged edges that the BMW has.

Mercedes AMG - NOT FOR RE-USE

The cabins of either are delightful places to be. They’re both based on their respective saloons, which is a great place to start. But there are enough smart and sporty bits to remind the drivers that they’re in something very special. There’s something truly special about the C63’s cabin, all gloss piano black cascading down the dashboard. The M3’s is more refined in such company but both are beautifully put together.

What does surprise is that it’s the M3 which has slightly more room for passengers, more space for luggage, better visibility and better infotainment. It’s actually the more practical of the pair.

It’s also the cheaper of the two to buy, although it will cost a touch more to run over three years. The C63 will be a bit cheaper and is also cheaper to buy on finance. There’s not much to choose between them as company cars, although we’ll say straight out that we’d be jealous of anyone who can wangle either of these as a company car.

Equipment levels – yes, they’re high on both. Fuel consumption – you don’t care, but they’re not bad as the table shows. Euro NCAP scores – you’ll care about those, and both cars are good for the top five stars.

Choosing a winner out of these is almost impossible since they deliver their incredible performances in two different ways. If you’re after a charismatic saloon with tons of power and torque with a glorious soundtrack and effortless style, then the Mercedes-AMG C63 is for you.

But if you want a saloon that comes alive the more you push it, and which is simply the fastest and most capable saloon out there – one that is faster than the Merc-AMG in either a straight line or through a series of bends – then it has to be the BMW M3.

Specifications: BMW M3

Engine size 3.0-litre turbo petrol

List price £59,850

Target price £54,764

Power 425bhp

Torque 406lb ft

​0-60mph 4.3sec

Top speed 156mph

Fuel economy 34.0mpg

CO2 emissions 194g/km

Specifications: Mercedes-AMG C63

Engine size 4.0-litre turbo petrol

List price £61,480

Target price £56,693

Power 469bhp

Torque 479lb ft

​0-60mph 4.3sec

Top speed 155mph

Fuel economy 34.5mpg

CO2 emissions 192g/km