They tested the vehicles in acceleration as well as handling around the track. They are fairly evenly matched both sporting twin turbo V8 powerplants and both having all wheel drive. The Audi is lighter by 180 pounds which is a substantial difference and helps offset its 25 horse disadvantage. The Audi is quicker in acceleration running the 1/4 mile in 11.68 seconds to the E63's 11.84. This appears to be all in the launch as the Audi gets to 60 miles per hour 2/10's quicker.
The 0-200 km/h (124 mph) sprint is even though meaning the E63 likely pulls slightly harder past the 1/4 mile. Regardless, two cars very close to one another although down low the RS6 seems to have a slight edge and the E63 likely has an edge up top.
What about on the track? The RS6 wins in this area as well running a 1:39.51 laptime to the E63 1:39.72. So, roughly two tenths here and the RS6 weight advantage paying dividends.
The cars are pretty even and AutoBild feels the same way but gives the edge to the E63. Why? Well, once again, I do not speak German but I'm pretty sure the extra half star awarded for the 'Emotion' category means they feel the E63 AMG S is more fun to drive. They are awarded even points everywhere else and the E63 wins with a 4.0 out of 5 to the RS6 3.9 out of 5.
With wagons of this caliber, you can't go wrong either way.