Having driven all of these cars, and taking the printed numbers with a grain of salt, I would say the R8 & M3 would lap a fraction faster than the C63. The C63 has a nice suspension but not quite the same as the others. Straight line the car is a beast! Auto is quick and pulls like a train.
I would have probably bought a C63 when I was shopping and chose the "IS" if it wasn't for the ugly interior and plain Jane exterior.