To challenge the M5's V-10, the S6 packs a V-10 of its own, but the Audi is able to extract only 435 hp, compared with 500 hp for the BMW. The S6 acquits itself better in the torque department, besting the M5's 384 lb-ft by 14 lb-ft. Mercedes comes the most prepared, at least on paper, with a normally aspirated, 6.2-liter V-8 that delivers a massive 507 hp along with 465 lb-ft of torque.
On the road, these differences in power and torque are less obvious than expected. After all, it's not only the numeric potential that matters but also what you can do with it. According to their manufacturers, the E63 can storm from 0 to 60 mph in 4.3 seconds, and the S6 performs the act in a less explosive 5.1 seconds. Our test results for the M5 put it right in between at 4.7 seconds. Of course, in the wet, the all-wheel-drive Audi wins the stoplight grand prix without even trying. On the autobahn, all three cars will beat the train and challenge the plane. Although the E63's maximum velocity is governed at 155 mph, AMG will reset the limiter to 186 mph if the customer pays big bucks for the 0-3-0 option [see page 88 of the July 2006 issue for more information]. The downside of leadfooting these beasts is a drastically reduced range and dramatically higher fuel bills. The M5 suffers more than the rest, because drivers invariably operate it in manual mode, and because it takes all 500 hp and the quickest shift setting to deliver the goods.
Visual judgments are more subjective. If you lean toward understatement, you may feel a little uncomfortable in the E63, which is dressed to kill. Its front spoiler was obviously designed to suck in air rather than to divert it, the small rear air deflector produces plenty of much-needed downforce, and the tapered sills help smooth the airflow before it reaches the razor-sharp rear apron. The two-tone, polished aluminum wheels are shod with eighteen-inch Bridgestone Potenza RE050 tires, 245/40 in the front and 265/35 out back.
Were it not for the aggressive-looking, five-LED running lights, the Audi would qualify for Performers Anonymous. The subtle visual modifications include a different grille treatment, four chrome exhaust pipes, slightly wider front fenders, flared lower door panels, and restyled nineteen-inch wheels fitted with Continental ContiSportContact 2 rubber (265/35 all around).
Although its visual impact was somewhat lessened in Europe by a look-alike sport package that is available for any ordinary 5-series, the M5 still stands out as one of the least controversial BMWs designed under Chris Bangle. It's a chunky piece, with a wide, low stance that spells presence with a capital P. The nineteen-inch wheels wear Michelin Pilot Sport footwear, 255/40 up front and 285/35 at the rear.
Inside, the M5 is somewhat stark, albeit at a high level. In addition to the love-it-or-hate-it iDrive, the quickest sedan from the Bavarian Motor Works offers a bewildering selection of setups. First, you must decide whether to change gears manually or automatically. That's an easy choice: in auto, the seven-speed SMG gearbox is still either unacceptably jerky or unacceptably slow. Second, you have to choose between 400 and 500 hp. Why? God only knows, but we suspect the engine always starts in four-fifths mode to curb its fuel consumption. Decisions three and four concern the shift speed (six to choose from) and the damper setting (three to choose from). What's next? Switch off stability control, or start fretting with iDrive? In total, there are twenty different settings that allow almost countless permutations. No, we didn't try them all. But we grew to like the combination of P500 (500 hp), M Dynamic Mode (heightened stability-control thresholds), EDC in normal damping mode, and S4 (fourth-fastest shift speed). You'll want to store your preferred mix and access it via the M button on the steering wheel.
The E63's owners' manual is as thick as the King James Bible, but mercifully, one can operate the car without it. The E63 still uses an older version of Mercedes' Comand system that lacks the central controller of the Comand in the latest S-class. So there are buttons galore. Like the face-lifted 2007 E-class, the E63 has received a much classier instrument panel, and the AMG's more supportive seats match the car's heady character. Aside from the new engine, the most significant change concerns the seven-speed manu-matic gearbox--with paddle shifters--in place of the departed five-speed. There are three shift modes: comfort (standard), sport (35 percent quicker), and manual (quicker yet). In manual mode, there is no kickdown and no automatic upshift. As before, the Airmatic suspension offers a choice of three different settings ranging from firm to compliant.
The cockpit of the S6 doesn't differ much from that in the A6. The leather sport seats, which strike a compelling balance between support and comfort, are the most welcome addition. We also like the supplemental digital speedometer and the top-grade materials. As far as fit and finish are concerned, this Audi is again more solid than the improved Mercedes and the comparatively drab BMW. Having said that, apart from the seats and the carbon-fiber trim, there is precious little radiating a sense of the occasion. Unlike the Mercedes, and other A6 models, the S6 isn't available with the desirable air suspension. Why? Because the engineers didn't want to add more weight to the already substantial 4486-pound total (versus 4160 for the M5 and 4035 for the E63), and because they felt that a coil-spring setup was more in line with the car's sporty character.
THIRD PLACE - BMW M5
A class master for many years, the BMW M5 has finally met its match. It's the M5's transmission that pushes the car down the rankings. SMG is wonderful for a track day, but it's a drag during the rest of the week. It's a shame, because the rest of the car is still dynamically spot-on. For instance, it's hard to imagine more communicative steering than the BMW's. The brakes also do a splendid job, although directional stability at very high speeds could be better and the ride comfort is acceptable only in comfort mode. As it happens, comfort mode provides the kind of suspension compliance that makes the car handle in a particularly creamy and predictable manner. At the limit, the M5 will instinctively attempt to oversteer. That's the good news. The bad news is that the car always goes through a phase of initial understeer before the tail commences its side step, so every extra square inch of tarmac helps, as does plenty of confidence.
So, the M5, at $81,895, comes in last, mostly due to SMG. Having said that, the six-speed manual transmission, which will be offered in the U.S. market later this year, may alter this ranking. But as it is, the ballsy BMW is too crude, too complicated, and too compromised to emerge as the best of this bunch.
SECOND PLACE - AUDI S6
The S6--like its big brother, the S8--benefits from a charismatic engine. Rated at 435 hp, the V-10 with Italian DNA features direct fuel injection, four overhead camshafts, and an intake plenum with two unequal-volume lungs. Drop the hammer, and the S6 catapults itself into action, generating tidal waves of noise that sound so physical they might result in the car's flight path being lined with leafless trees and featherless birds. The gearbox programs are mapped much more closely together than those in the Benz, but manual mode further speeds up the gearchanges, and in the sport setting, the engine revs greedily to its 7000-rpm redline. Thanks to Quattro, traction is never an issue, and grip is magnetic. Torque is split 40/60 percent front to rear, but this rear-wheel bias is recalculated at the first hint of wheel spin. The Audi has the most riveting brakes, and its steering is reassuringly competent in managing the sometimes antagonistic propulsion and direction-changing duties.
We expected the S6 to be notably slower and less involving, with more androgynous handling qualities and less feedback overall. But we were wrong. Despite the near total absence of drama, its set of reflexes is complete. Quattro is a bonus not only in winter or when it rains: it also ties the car down well through dips and brows, makes carving the twisties much more relaxed, and always--always--puts the power down. Instead of bothering you with weight distribution or traction-control issues, the S6 simply goes where you point it. No, power oversteer is not easily induced, but when you whip all three cars through a wet corner, there is one clear winner. And at an estimated $75,000, the Audi is the most affordable supersedan.
FIRST PLACE - MERCEDES-BENZ E63 AMG
What makes the E63 so special is the blend of its abilities. For a start, it's a particularly emotional machine-mean-looking, acoustically overwhelming, and very fast, yet it can be either velvety smooth or bondage brutal, whichever you wish. True, the stability-control warning light may flash in the wet at 125 mph, but you won't feel more than a tug or a kick, and then it's full urge again all the way to the 7200-rpm redline. Unlike the supercharged E55, which was so pumped up with hormones it could hardly accelerate in a straight line, the follow-up model is a lot more relaxed, more sure-footed, and quite a bit quicker. By a wafer-thin margin, the Benz has the most compelling engine. It wins the torque trophy and the acceleration medal, it sounds awesome, it's mated to a transmission that confines itself to only three shift programs, and its relentless push extends into the triple-digit speed zone. What this car needs to move even closer to perfection are brakes with extra staying power and steering that can do more than change direction.
Even under pressure, the nose of the E63 finds it easy to stay close to the apex. As a result, the driver is more inclined to light up the rear tires in crowd-stopping fashion. The trouble is that you can slide the Benz only with stability control off, so there is no intermediate safety net such as M Dynamic Mode in the M5 or traction control off in the S6. Unlike the BMW, which feels a little twitchy as it nears the limit of adhesion, the AMG hugs the tarmac. There is also less lift-off weight transfer, less acceleration squat, and less brake dive, and, despite the subdued body movements, you always know where you are on the speed and g-force map.
At an expected $85,000, the Benz digs deepest into the budget, but it is worth every penny--against the stopwatch and in smiles-per-miles currency. It wins on merit and appeal, even though it surpasses the S6 only by a whisker.
The fact that the M5 has fallen so far so fast tells you three things: That this is an extremely fast-moving business. That even a well-founded status quo can be eroded by clever evolution. And that the big-engine-in-a-mid-size-car game is more competitive than ever.