Neckarsulm, Germany – The forecast called for sleet, and under normal circumstances this might have been a disappointment. I was scheduled to go tearing about the German countryside in a brand new Audi packing a Lamborghini-based V10. Secretly though, I was kind of thrilled.

Quattro weather! While other 400-plus-horsepower sedans would be tiptoeing along trying to maintain traction, the Audi S6’s all-wheel-drive would be unfazed, putting the power to the ground through all four contact patches, distributing power where it was needed, with scant drama despite the car’s power output and the slick roads. And so it pretty much proved, despite roads that were only damp in some spots: whether we were charging along the left lane of the autobahn, sweeping along two-lane roads, or testing out the car’s handling on a racetrack, the S6 was stable, confidence-inspiring, and wickedly fast.

Despite all of its other features, this is a car that is totally defined by its engine. The 5.2-litre V10 nestling behind the big single-frame grille shares its architecture with the 5.2-litre V10 in the Lamborghini Gallardo, while being almost a totally different engine (all of its parts are different, and it features direct injection that improves efficiency). While it produces less power here than in the Italian supercar – a "mere" 435 horses compared to 500-plus in the Lambo – it delivers that power with an Italian flair. It zings up to its redline with impressive gusto, and it produces power all over the place: enough torque to screech all four tires from a dead stop, and enough high-end go to keep up with, and blow past, all but the fastest autobahn traffic.

And then there’s the noise: a throaty roar through the midrange that switches over aggressively into a top-end shriek that gives the S6 an aural signature unlike any other German car. Even though the BMW M5 also has a V10 (and even though it produces 507 horsepower), it doesn’t sound quite this exciting. It sounds sufficiently cool that you find yourself always driving around in a lower gear, using the shift paddles on the back of the three-spoke wheel – they light up at night – how cool! – to keep the engine spinning in the noisy part of its power band, especially when you’re blasting past rock walls or roaring through tunnels.

As such, the S6 is an edgier, more aggressive sort of performance sedan than we’re used to from Audi. It surges forward on light throttle openings, and the quattro drive system distributes more power to the rear – 60% in normal conditions – than previous models. The six-speed automatic transmission shifts with authority, whether you’re just puttering around or surging ahead on full throttle in sport mode. Add to that a non-adjustable suspension that’s been significantly stiffened from the stock A6, massive 19-inch wheels with low-profile tires, and recalibrated steering, and you have a pretty wild ride. One that’s at its best when you’re driving it aggressively, and which isn’t at its best clumping around city streets. In traffic, the touchy throttle makes driving smoothly difficult, and the suspension can feel uncomfortable on rougher roads.

That’s not to say the S6 is an uncomfortable car: far from it. Indeed, as well as being the fastest A6 you can currently buy, it’s also the most luxurious. Beyond still being automatically shifted (the M5 has a sequential manual), the S6’s interior comes fully loaded. The seats are covered in leather and have bigger side bolsters and integrated headrests. They, and the steering column, are adjusted electrically through a wide range of possible driving positions. A fabulous Bose 6-disc CD stereo is standard equipment, along with a navigation system. Electronic climate control, heated seats, and a big moonroof are all standard equipment.

The cockpit is draped in gorgeous aluminum and dark-coloured wood (or optional carbon) trim, and contrasting stitching and subtle S badging rounds out the package. As you would expect, the perception of quality is excellent, with all of the pieces having an impeccable finish, panel gaps that can barely be measured, and a general air of richness pervading the roomy cabin.

As with all A6s, the S6 uses Audi’s MMI interface, a knob flanked by four buttons flanked by another eight and a volume knob, to control all of its entertainment and navigation features. The navigation system has been further improved with the addition of bird’s-eye views of intersections (like Infiniti does), and the European map disc has 600,000 points of interest (shift into reverse and you get a rear-view camera). That, and the other features, remain fairly easy to use once you’ve played around with the system for a few minutes, but programming radio stations isn’t any easier than BMW’s iDrive, which has fewer switches. On the other hand, the implementation of MMI-like controls for the climate system is downright brilliant: the climate knobs are themselves surrounded by buttons for the fan speed, temperature and seat heater, and work in much the same way, using the same dashboard display.

Exterior changes are subtle but noticeable to a trained eye. The wheel arches have been flared by 14 mm, which combined with the larger wheels and tires – the wheel design is new, of course – makes for a more aggressive stance. There’s a new front bumper with LED "eyebrows" over the air intakes, giving the car a really mean look. Out back, there’s a subtle spoiler and four oval tailpipes. Some interesting colour choices are also available, though all of the test cars in Germany were painted silver or black.

As a pure sports sedan, the S6 is in a bit of a weird place. On narrow European roads, there were times where it felt too big to exploit all that power and grip, but it should do just fine in North America. The automatic transmission will certainly be a downside for some, though I have no complaints about how quickly it responded to manual shifts, either with the tiptronic function on the console or the paddles behind the steering wheel. Compared to the other players in this class, it’s down on power, too, and while it doesn’t feel slow at any time, there will be customers for whom only the fastest or most powerful car will do.

Other downsides include steering that’s as accurate as you could hope, but has a noticeable "step" in its power assistance, which is contingent on vehicle speed: it’s almost too light at lower velocities, but weights up perceptibly, sometimes in the middle of a corner. The brakes – massive 18-inch units up front – are powerful, but they can feel a bit grabby at lower speeds. A price to pay, I guess, of their incredible stopping power and reassuring stamina on the autobahn. And, oh yeah, the V10 badge on the side of the car seems a bit gaudy given how subtle the rest of the styling tweaks are. The biggest downside will be for wagon enthusiasts; while an Avant version of the S6 is available in Europe, it won’t be coming to North America.

As an all-around fast sedan for our market, though, the S6 offers a killer advantage in the form of its quattro all-wheel-drive. Other competitors in the class may be more powerful, or have slightly purer controls, but none offer the S6’s stability and all-weather capability. And none of them have an engine that combines the best of German and Italian personalities and sounds the way this one does. With even the high-end sedan market becoming increasingly crowded with similar products, that has got to be worth something.

At a glance: 2007 Audi S6

Price: $105,000 (estimate)

Engine: 5.2-litre V10

Fuel consumption (European city/highway/combined): 19.7/9.7/13.4 L/100 km

Competitors: BMW M5, Mercedes E55 AMG, Cadillac STS-V

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