You might expect, given that this new Audi S8 is powered by a V10 engine normally found in a Lamborghini, that this is going to be a tale of statistical superlatives, of mindbending speed and awe-inspiring abilities. But it’s not, for that is not the Audi way. The S8 may have 444bhp, but expect it to explode down the road like, say, a Mercedes S 55 AMG and you’re going to feel sorely let down. And expect it to handle like that other V10 über-saloon, the BMW M5, and you won’t feel much better.

So forget right now any notion that this is a supercar that just happens to have four doors and a big boot, for it is nothing of the sort. Yes, it will hit 62mph in 5.1sec and accelerate hard to its 155mph speed limiter, but in the 21st century these are increasingly everyday figures and a poor guide to the appeal of this new car.

The most important thing to know about the S8 is that all those things that make the standard A8 such an attractive proposition have been retained or enhanced. For all its extra speed I could detect no degradation in either ride or refinement: this is a car that recognises that, Lambo motor or not, it remains an executive saloon. There’s the same exquisite interior, albeit with sports seats and carbon fibre trim, the same MMI operating system that still makes all others look flawed and fiddly, and the same spacious cabin.

What it adds, as well as the 5.2 litre motor, is specially stiffened suspension, optional ceramic brakes, a purposeful grille and those beautiful, vast 20in wheels. Its quattro four-wheel-drive system has also been re-engineered so that instead of the engine splitting its power equally between the front and rear wheels, the split has a 60/40 rearward bias to counter a stream of criticism from people like me who say that all Audis feel nose-heavy.

It still feels nose-heavy. In fact, now I think of it, it feels just plain heavy. When you add the weighty four-wheel-drive system to that vast motor, you have the thick end of two tons of car.

Like all big, heavy cars the S8 needs space and lots of it if its true talents are to shine through and, on a dull winter’s day in the industrial north of Germany, space was a wretchedly scarce commodity. But I did find an autobahn long, straight and deserted enough to know that an unrestricted S8 would fly past 180mph and that the V10 engine is, like the car itself, an understated masterpiece. In a Lamborghini Gallardo it howls and roars like any true supercar should, but it has been slightly detuned for the S8, despite being enlarged from 5 to 5.2 litres.

But while its bite is a little blunter and its bark rather more muted, so it is also much more flexible and suited to a large saloon. And with a paddle-shift auto flicking through its ratios faster than I could change gear by hand it feels quick enough to satisfy most tastes.

Of course I’d rather drive a BMW M5, particularly as its V10 has more power, more gears and a price tag more than £6,000 below the £70,000 that Audi estimates the S8 will cost when sales start in June. But the S8 is more closely aligned to the 7-series BMW, and there’s not one of those I’d even look at before stepping smartly into the Audi.

As for Mercedes-Benz, we have yet to see any AMG versions of the new S-class, but I recently spent a week in a previous-generation 500bhp S 55, and while its performance appeared to be dramatically superior to the S8’s I don’t think it was enough to justify the £20,000 price gap.

Besides, I’d be amazed if the Audi proves anything less than fabulous to own. It’s the best looking executive car on the market and that’s something you’ll always feel good about. It is calm and soothing, yet when you press the start button and hear the uneven beat of the V10 as it comes to life, it is special, too. These may not be the attention-grabbing talents you might expect from such a car but, take it from me, they are no less compelling for that.

VITAL STATISTICS

Model Audi S8 quattro
Engine type 5204cc, V10
Power/Torque 444bhp @ 7000rpm / 398 lb ft @ 3500rpm
Transmission Six-speed automatic
Fuel/CO2 21.0mpg (combined cycle) / 322g/km
Performance 0-62mph: 5.1sec / Top speed: 155mph (electronically limited)
Price £70,000 approx
Verdict Compelling, in an understated Audi way
Rating 3/5

THE OPPOSITION

Model Jaguar XJR £61,995
For Lightweight aluminium construction, fine ride quality
Against Its design looks 20 years old

Model Mercedes S 55 AMG £89,745
For Massive performance
Against Massive fuel consumption