Audi's A6 is a well-liked luxury sedan around these parts. Outstanding dynamics, unique/good looks and a high-quality interior have left all who've driven it impressed. Our full test of a 2005 Audi A6 3.2-liter V6 Quattro revealed that about the only thing lacking was a bit of thrust.

So when we heard that a 2006 Audi A6 with the 4.2-liter V8 and Quattro all-wheel drive was coming to roost for a spell, we got excited. An 80-horsepower boost just had to cure the problem, right? After all, the 2004 Audi S4 we last tested, which had essentially the same engine, left quite an impression, and plenty of melted rubber, in its wake.

In A6 form, the 4.2-liter DOHC five-valve-per-cylinder V8 engine puts out 335 horsepower at 6600 rpm, while 310 pound-feet of torque arrives at 3500 rpm. Our test car came with a Tiptronic six-speed automatic — the only gearbox available.

It's not particularly cheap, though, as the base price of a 2006 Audi A6 4.2 with standard Quattro rises to $54,490, compared to $44,690 for a 3.2-liter V6 Quattro. With options, our 2006 Audi A6 4.2 Quattro test car tripped the price-o-meter to the tune of $64,840.

Ss for days
Audi's approach to performance is broader than most, and results in a confusing array of "S" designations. Our test car featured the $2,950 S-Line package, a sport suspension and appearance option that can be added to any A6. Unique wheels and 18-inch tires are paired with a "stiffer" suspension that sits 0.8 inch lower than usual. Also included are nose and tail mods, interior trim upgrades and S-Line badges. Engine and brake tweaks are not part of the S-Line program.

So now here's where the 2007 S6 fits into the mix: The V10-powered S-monster we drove in April was developed in-house and will be built on the same Neckarsulm assembly line alongside regular A6s. Tires and brakes are larger still and it all sits 1.2 inches lower than an A6. The full monty would be an RS 6, if there were such a thing, but there isn't — yet. RS models, like the thrilling RS 4, are built off-line by Quattro GmbH, Audi's in-house tuner group similar to BMW's M and Mercedes-Benz's AMG. Like we said — quite an array of S-designations.

Now that that's out of the way, back to the S-Line: Ours sported 245/40R18 Pirelli Rosso summer performance tires. Those of you who ply the northern snowy realms need not worry, as the S-Line package can be had with all-season tires in the same size.

Track daze
Our Rossos and the S-Line suspension did a pretty decent job of hanging on to the asphalt, as our 0.82g skid pad and 65.3-mph slalom numbers attest. Indeed we found this A6 to be nimble, neutrally balanced and even steerable by throttle to some extent.

But in cruise mode, we were bothered by overboosted steering that bordered on vague, especially at residential speeds. And all roads seemed a bit lumpier in the S-Line, as passengers commented that the busy ride didn't seem to match the lush interior they were strapped into. What do they know? This is a driver's car, isn't it?

Well, maybe not. While the 4.2-liter engine was willing enough, and sounded bitchin', its ableness was perhaps handcuffed by a recalcitrant Tiptronic gearbox and the car's 2-ton-plus curb weight.

Indeed our car's as-tested 4265-pound heft was 250 pounds over a 2006 V6 A6 Quattro's manufacturer rating of 4012 pounds. V8 competitors from Mercedes and BMW recently tipped our scales at 4003 and 3941 pounds, respectively.

Acceleration seemed leisurely at times as the tranny slurred its way to the next gear and was reluctant to kick down. Manual mode helped, but our test car did not have the more engaging $690 paddle-shifter option. Audi must have noticed this, too, as it has added the steering wheel shifter to the S-Line bag of tricks for 2007.

Our quickest track run to 60 mph, an unremarkable 7.1 seconds, was only slightly quicker than the 7.9-second run that our A6 3.2-liter V6 test returned, and was nowhere near the low-5-second capability of the similarly engined Audi S4 Quattro equipped with a six-speed manual that's unavailable on the A6.

For perspective, same-day tests of similarly priced BMW 550i and Benz E550 Sport models produced 5.6- and 5.2-second blasts, respectively. For further perspective, we've pedaled a V6 Toyota RAV4 to 60 mph in the same 7.1 seconds as this V8 A6.

I could've had an S6
As much as we liked the handling boost provided by the S-Line bits, the package writes a performance check that this engine can't cash, creating a personality mismatch. Don't get us wrong: The 4.2-liter V8 still makes the A6 an even better luxury sedan for plying the country clubs and gobbling up the miles. And at 17 city/23 highway mpg, it gets good enough fuel economy to avoid the gas-guzzler tax to boot. Still, the V8 powertrain, despite a noticeable gain over the 3.2-liter V6, simply doesn't deliver the grin factor.

Luxury is still the A6's forte, so fans who can afford the V8 A6 might consider skipping the S-Line package, while the performance-minded should save their money and wait for the V10-powered S6 — if they can save $10 or 15 grand more, that is.