The people that recognize that the M3 shouldn't be cross-shopped against a high hp american car have it right.
Also bear in mind that forced induction cars are easy to add significant amounts of power to if that's your thing. 335's can be tuned to 400hp fairly easily, I'd imagine the new M3 can be tuned to 500+ safely because BMW is not going to release the car on the limits of safety boost-wise.
600hp is still totally usable BTW, maybe not so much on small city streets, but definitely either a highway or track environment. I've driven cars with that much or more on roads and on track and you just have to realize the throttle is not an on/off switch...
My 2 cents.