I'm not sure the RS5 will have that much power, and why.
The M3 have 420 hp and weigh something like 1600 Kg, rumour say the next M3 will have a tuned 335i inline 6 engine.
If Audi want a BMW M3 killer that handle's, reducing weight is the way to go, not adding more power.
If Audi put in the 3.0TFSI V6 Supercharged engine with a bigger supercharger (or Bi-turbo's on top in the V of the engine) with 400+ hp and keep the weight close to 1500 Kg that would be a M3 killer.
Nissan is showing with the GT-R that a V6 engine is enough.
Jarod.