Despite at least 73hp advantage over the M5, the RS6 will hardly put the same amount of power on wheels.
As seen in recent test (http://www.rri.se/popup/performanceg...p?ChartsID=281) , Audi's belong to the worst performing cars.
So, as M5 can put around 93% of its engine power to the wheels (471hp), the RS6 with 580hp will put down roughly 481hp (only 83%)...
I know the 4WD has many advantages but to me this is a bit too much..