Engine: 4,163cc, V8 cylinders, 32 valves, 420bhp at 7,800rpm, 317lb ft at 5,500pm
Transmission: six-speed gearbox, four-wheel drive
Performance: 155mph, 0 to 60mph in 4.7 seconds, 20.9mpg official average
Can an Aston Martin and an Audi occupy the same sentence? It looks like they just have, just as they occupy adjacent slots in an alphabetical list of car prices. But there is more reason than mere etymological coincidence. Take the newest examples of both brands.
Last year we covered Aston Martin's new Vantage V8 in these pages, thrilling to its engine note, loving its combination of searing high-revs power and easy low-revs cruisability. And that magnificent engine bears a remarkable resemblance to that of Audi's new RS4, the fastest road-going Audi ever - and yours for £49,980.
The Audi's engine is a little quieter most of the time (although it, too, has the Jekyll and Hyde personality split brought about by an exhaust bypass valve), but the character, the crispness, the fabulous excess of energy, all are shared.
The RS4's figures are astounding. Eight naturally aspirated cylinders, 4.2 litres, 420bhp pouring out to the wheels. (Thus is the Aston upstaged: it achieves "just" 380bhp from its 4.3 litres.) That Audi power is fed to all four wheels, because this is a quattro-drive. Then there's the speed, electronically limited to 155mph but potentially rather more, and the ability to pass 60mph after 4.7 seconds.
And then there's the engine's ability to scream to stratospheric heights as it performs these feats, levelling off only when the rev-counter reads 8,250rpm. That's Aston-like, too, except that the British car isn't quite so rev-happy (only 7,500rpm, poor thing). No Audi has performed feats like these before.
This latest RS4 is far removed from the already rapid, also V8-powered, S4, not least because it has a six-speed manual transmission instead of a video-game automatic. But the last RS4 was a big disappointment. It had huge pace from its twin-turbo V6, but there was no drama, no thrill, no sense of bonding with the machine.
It took the RS6, based on the old-generation A6 and powered, like this new RS4, by a hefty V8 with not a turbocharger in sight, to show that Audi could once again make a really rapid car that is also fun to drive. Making the driver feel involved in the driving process, generating satisfaction from the experience instead of trying to numb it, these have long been Audi blind spots.
Yet it hasn't always been like that. The original Quattro was a highly exciting car. But after this, Audi seemed to lose the knack.
The RS6 was such a breath of air that it almost seemed to be an Audi mistake. To drive it was to drive an Audi in a roadscape cleared of fog, in which everything happens instantly and sends back messages as to how the happening is happening.
Into this mould is cast the new RS4, as different in character from the not-really-sporty S4 as it can be. Unlike the RS2 and previous RS4, which were estate cars (and probably the most rapid of the genre you could buy), this RS4 is a saloon. Its body is wider than a regular A4's, thanks to flared-out wheel arches; the front wings are of aluminium, as is the bonnet.
The engine has FSI direct injection, as is now the Volkswagen Group way, and an extraordinarily high compression ratio of 12.5 to one. It has race-specification connecting rods, so it will stay together at the high speeds that are the secret of its power production.
Its pistons move up and down at a maximum rate of 25.5 metres a second, about the same as a Formula One car's. Each cylinder sucks air up to 70 times a second during which time the ignition system supplies 550 sparks, and the lubrication system is designed to cope with a 1.4g cornering force before all the oil ends up out of reach of the oil pump.
And here's an Audi first, an admission at last that really fast cars work better when the rear wheels do most of the work of power transmission. Left to its own devices, the system directs 60 per cent of effort to the rear instead of Audi's usual 50 per cent. This proportion can alter according to the amount of grip available to each wheel, but the starting point is that of a proper sports car with a little bit of power oversteer.
What else? Enormous brakes, with eight-piston calipers at the front, and the Dynamic Ride Control first used on the RS6.
Time to try it out, beginning by pressing the start button that's now de rigueur for a sporting car. The V8 woofs into life, ready for the off. Into first, second, third; the RS4 is immediately very rapid, pulling hard - harder than the Aston - from low revs right through to that stratosphere. But there's something odd about the accelerator response. The first part of the pedal's movement is unresponsive, making an accurate blip hard to meter when you're trying to smooth a downshift. Also, if you throttle back suddenly for an upshift, the whole driveline oscillates springily.
Then I press the Sport button on the steering wheel. The accelerator's response becomes crisper, cleaner, easier to fine-tune, although the change in mode is progressive enough not to cause a sudden surge of energy while the new settings take effect. And the seats, if you have the optional sports seat pack, narrow themselves by 15 per cent to clamp you more firmly for the sporty drive you're about to have.
I'm not sure about that last part. If you've been happy with the way the seats already were, the sudden intimacy is unsettling. I found myself readjusting this electric lateral support back to its former position.
Into a corner, feel the steering connect precisely with the road, feel how easy it is to point into a corner and adjust the line with steering or accelerator. It's transparent, it draws you in, it talks to you; it powers out of a bend like a BMW M6 but without the fear of an incipient powerslide and sudden electronic intervention. It is, in short, so unAudi-like that, deprived of visual clues, you would not guess the make.
It also rides very well, better than any other Audi A4 in the model hierarchy, whether on standard 18in wheels or optional 19in ones. A few laps of Pirelli's test track at Vizzola, near Milan, confirmed how agile, how controllable and how hugely adhesive this car is. It is, in fact, the best Audi ever.
BMW M3 £41,875
Only six cylinders and 343bhp, but what a crisp, beguiling engine. Ride is too firm, but on the right roads this two-door coupé is a fabulous drive. Based on previous 3-series; production ends soon.
CADILLAC CTS-V, £45,000 approx
Left-hand-drive only, but this razor-edged, Corvette V8-powered ultimate CTS takes you where you never thought a Cadillac could go. Cabin feels cheap at this price, but terrific rear-wheel-drive fun.
MERCEDES-BENZ C55, £48,790
Another V8, less racy than the Audi's. Automatic transmission takes the edge off the sportiness, but this top C-class is an understated and rapid performer, albeit overshadowed by the RS4.