I had the opportunity to drive a friend's new (2003) 6 speed M3 the other day with the following assessment.
The car is grossly overrated. Compared to a 330, the car is noisy, shifts badly, and rides like a rock. The brakes are great, the car understeers significantly, and the power, while good, is not really all that great. Based on seat of the pants feel (and looking at the speedo) I would say that the thing is not significantly faster than my WRX (stock plus Cobb stage 1) to 60. The traction control is EXTREMELY intrusive...any amount of wheelspin results in a power cut for what seems like an eternity. I took it up one long freeway hill where I could really give the high RPM power a chance and found that the thing kinda slowed down a lot at about 110. While the powerband is wide, it's not really strong below 6 grand and the pull from 6-8 is ok, but nothing to get excited about.
Compared to my '01 C5...there's little comparison. The Vette has so much more torque the fact that the power ratings are similar is almost irrelevant. On the same hill where the M3 kinda pooped out at 110 the Vette is pulling strongly past 130. The other thing is that this little car is a real porker, especially compared to the previous generation M3.
All in all I would think that in any contest of speed other than acceleration beyond 100 MPH, a lightly modified WRX would be more than a match. From my experience driving the previous generation M3 it seems that the older car would be a much more formidable opponent on a twisty road than the new M3:
-the handling is significantly better
-the car is dramatically lighter
-power below 6k RPM seems stronger
-traction control intervention is not an issue
-brakes are just as good
In terms of real world competition I would say that the new M3 has a very limited set of competencies. It has good top end power, but other than that it seems that a WRX would be pretty darn close on a winding road and a Vette will absolutely kill it at high speeds.