I had a E92 M3, now a 1M. (HP4 to be expected late january, early february 2013)
Acceleration will be on par at 200 km/h, over this speed the M3 will slowly walk away.
The main reason that the M3 will walk away is;
1 It has got more HP
2 The drag coefficient(Cw) for the 1 M is far more worse (this has never been mentioned before, but it is likely the most important reason)