either. The suspension is considerably softer, certainly in the A6. 420hp in the S6 does not pull like the RS6 and handling (having driven an S6 today actually) from my seat of the pants anyway is much flatter/tighter in the RS6. I have driven all the above and you are nuts. By the way i get mortifying gas mileage. Not a case of me loving my car and blinded by that either. I would lap a C6 A6 on the track.
Mentioning another new Audi the S5 did impress me following it on the track...handled very well in the turns certainly better than my car watching it from behind and i could barely catch it in the straight so that car I think is very well done.
I have watched plenty of videos of RS4s dueling with Rs6s with professional drivers...there is not a significant difference in a pros hands.

2003 RS6 Daytona Gray, Silver Interior
RNSE
RS6 logo matts (waste of $$$)
RS6+ OEM 19" Titanium 5 spokes(summer)
RS6+ Dead Pedal
Stuck with it forever-depreciation rocks!
Go Gators
Future
R8 Phantom Black/Silver or Ibis- In longggg line
Former
2000 TT Coupe Neiman Marcus #25/100
2001 BMW X5
1994 Audi Cabriolet