C63's are quick man....but I would still take the M3. If I wanted super fast I would have purchased the Z06.
On to your question hit up a dynojet in your area first and see where you are baseline....then we will know what gains you need.
your location says "cool" so I'm not sure if they have dynojets there anyway
335i Coupe, Titanium Silver, Black Leather, Alum. trim, Auto, Sport Pkg, Premium.
Ordered: 5/15/07 Entered Production: 6/21/07 On Franconia: 7/4/07 Unloaded in SC: 7/18/07 VPC: 7/18/07 Picked Up: 7/25/07