If you're a keen reader of Motor Trend, you might have noticed two Easter eggs we placed in the November 2013 issue, "hidden" on a one-page addendum to our annual Best Driver's Car feature. There, nestled among a long list of 70 lap times we'd recorded at Mazda Raceway Laguna Seca, were two that, for all intents and purposes, had no business being there (partly because we printed incorrect times for both). We hadn't covered the cars prior -- at least not together -- so you probably thought, "I don't recall a track test on the Audi RS 5 and Mercedes-Benz C63 AMG 507." Well, no need to recall a thing, as voila! the wait and confusion are over. We meant to run this comparison a while back, but we took the Audi on, how should I say it, a bit of a "field trip," so we had to hold tight till we got a replacement. (Sorry, Audi!) Thus, the lap time is from our initial 2013 RS 5 loaner, while the test numbers reflect a subsequent 2014 vehicle. (There are no notable differences between the model years.) Without further ado, let's meet the players. 2014 Audi RS 5 Mercedes Benz C63 AMG 507 Edition
The Cars
The $78,320 Audi RS 5 entered this comparison as a slight underdog to the $90,810 Mercedes C63 507, thanks to a naturally aspirated 4.2-liter V-8 whose 450 hp and 317 lb-ft pale in light of the Merc's monstrous 507-horse, 450-lb-ft 6.2-liter. Not only is the all-wheel-drive Audi less powerful than the rear-drive Benz, it's also heavier -- 4027 pounds versus 3952. Both feature seven-speed transmissions, with the Audi's S tronic dual-clutch boasting quicker shift times to the Benz's untraditional wet-clutch automatic. The $12,490 price gap between the two is sizable, represented for the most part by the C63's $9750 P61 Edition 507 package, which includes the 56-hp, 7-lb-ft output upgrade as well as a higher 174-mph top speed, 19-inch forged wheels, and the C63 Black Series' aluminum hood and bigger brakes, but not its brake pads. Throw out the 507's superfluous items not optioned on the Audi -- the $3950 matte paint job, $850 illuminated doorsills, $1000 black wheels -- and the delta, at $6690, becomes less glaring.
The Road
Senior features editor Jonny Lieberman and I headed for our favorite 50-mile test loop through and around Malibu, an ideal mix of freeway, demanding mountain roads, and coast highway. The RS 5 emerged as the firmer rider of the two, steadily relaying a detailed feel of the road for better or worse, while the C63 rode softer and more composed, with no noticeable deficiency in handling. Given the Benz's dynamic prowess, its ride comfort was impressive, reminiscent of a Panamera. The 507's steering was deemed superior, offering excellent feel, light but not too light weighting, and nice, organic sensations. In contrast, the Audi's helm came across heavy and numb, and definitely the weakest part of its formidable chassis.

I say formidable because, as its 0.99 g of max lateral accel suggests, it delivers tenacious grip. The "party trick," as Lieberman notes, is the sports rear differential. "When you're in Dynamic mode, it overdrives the outside rear wheel through corners, meaning that once you've reached the apex of a turn (or really, even sooner), you can just bury your right foot. It's very counterintuitive, and frankly a weird way to drive, but it works." That said, the RS 5 does relay its mass to the driver more than the 507 does. The Audi always feels glued to the road, but you feel the weight transfer between the big 275/40R20 Pirellis as you work the car to "unglue" it through turns. The Benz, conversely, at 0.91 g of max lateral acceleration, just glides along the road, coming across lighter and nimbler. It should be noted, too, that the 507's sport seats and driving position were rated above the Audi's. Per Lieberman, "In the Audi, I was getting flung about when the road got bumpy and twisty, making me wish for much more shoulder bolstering." Under aggressive braking, especially when the brake zone featured bumps or slight bends, the Audi proved more stable, staying flatter and exhibiting less drama. Both registered curt 60-0 stopping distances: 103 feet for the C63 and 104 feet for the RS 5. That's not to say the C63 didn't offer great brake feel. With lovely, high engagement that allowed gentle breathing on the pedal to start the slowdown process, yet prodigious bite when really needed, the Benz's binders were nothing short of excellent. Ditto for its 6.2-liter. Man, what a motor. Revs above 7000 rpm, yet has massive low-end grunt and sounds like a '60s musclecar. Lieberman: "Just so much power, everywhere. Revs like crazy. All the torque you'd ever want is on tap. Angus MacKenzie, MT editor-at-large has said that if they ever build an engine Hall of Fame, the AMG M156 deserves a place in it. Every time I drive this motor, I see how much wisdom there is in that statement." The RS 5's relatively puny 4.2 probably would make it into the hall as well. After all, any V-8 that spins north of 8000 rpm is all right by us. Compared with the 507's low-end-torque-monster 6.2, the Audi's 4.2 is reminiscent of what it was like matching a Honda S2000 with a Porsche Boxster. You can go just as fast; you just have to keep the tach needle bouncing about the big numbers. And keeping the Audi's tach needle where it needs to be couldn't be easier, mostly b ecause you don't have to do anything. The S tronic intuitively does it for you, whether performing seamless shifts in Drive or firing off millisecond gear changes in Sport. Simply put, it's a noticeably better transmission than the Benz's MCT. Thus, there's no surprise the RS 5's 0-60 (3.9 seconds) and quarter mile (12.3 seconds at 112.2 mph) runs were just a tenth behind the C63's (3.8, 12.2 at 117.4, respectively).

The Track
With the 507 emerging as our road favorite, it was time to hit the track with our resident racer Randy Pobst to see if it could maintain its thin margin over the Audi. Pobst went out in the Merc first and set a fast lap of 1:43.45 around Mazda Raceway Laguna Seca's challenging 2.21 miles. All smiles? You could say that. "Oh, holy cow!" said Pobst. "Really strong driver's car. In its weight category, it definitely runs with the 911. It creates a lot of confidence, giving the driver the ability to place the car really well, because it's so well-balanced. When the spring forces are loaded up on one side and then unloaded, it does it slowly and predictably; it doesn't pop back, and the car does not snap. The damping is really well-done, and that package makes it a very good driver's car." 2014 Mercedes

Given how high Randy was on the 507, we figured the less powerful, heavier RS 5 had no shot. We couldn't have been more wrong. Posting a best lap of 1:42.97, it was 0.48 second quicker, but Randy's comments suggested more like 4.8 seconds. "The R8 should be half this good! This car is fantastic. I adore it. It does such a great job utilizing all-wheel-drive traction off the corner, with zero push. You just drive in there and you think it's too early, but you just floor it and you're like, man, I should've gotten on the gas sooner. And no push, no oversteer -- it just drives right out of there, beautifully carving an exit line, using all the power. The gearbox is also very friendly. I just got more confident with carrying speed in and trusting the grip." Indeed, Pobst was able to dive deeper into the corners in the Audi and then carry more speed through the turns. That's where the Benz lost time, albeit not that much. Had it not been for the 507's underhood advantages, which gave it the drop exiting corners and on straightaway Vmax, the RS 5 would have extended the gap.

The Decision
The RS 5 is a balanced blend of rally car, road racer, and GT, and in many ways it's the cooler, more desirable machine. Its stance is meaner and stronger -- the sheetmetal seemingly shrink-wrapped over the five-blade 20s -- while the Benz looks like it's a big engine stuffed into a small car. And seeing the RS 5's bold mug, with the big black grille and brake ducts, in the 507's rearview makes you want to switch driver's seats. Then there are the Audi's screaming V-8, quick-firing DCT, Quattro AWD, and superior track time. But the 507 is more fluid on winding roads than the RS 5, which feels robotic in comparison -- like going from an analog 911 to a digital GT-R -- and it's certainly no slouch at the track. The Audi might be quicker up and down a mountain and around Laguna, but it's more of a ride-along. The Benz is engaging, inviting you to join in and experience the party. And we always prefer being the life of the party.