If the M3 does 0-60mph in 5.2 seconds, than I know that I can beat that with the M5. I have recorded 0-60mph in the sud 5 second range regularly. My best is 4.78 seconds with some wheel slippage, but who cares when the speed is of this magnitude.
The M3 is lighter and will corner a little bit better is my guess, but in a straight line, it will be more driver dependant than the car. Anybody have an idea what the top end is estimated to be with the speed limiter removed for the M3?