[SlowToady]

The M3 is a hell of a car; docile around town and pretty darn fast when you put your foot into it--either on a straight or in the twisties. The straight 6 also has better torque/hp curves than the 968/951/944 (IMO, it drives how I like it..), and like was mentioned, has power everywhere, in every gear.

Upgradeability? Dinan makes a supercharger for the M3 (I know I know, cost..).

As far as building a 951 that will smoke an M3, that could be reversed. I've ridden in a supercharged M3 that was so fast I thought I'd seen God. And I more or less grew up around fast cars, especially since my brother did custom stereo installs for United Audio, Really Fast Cars would come in all the time. We drove a 550HP Twin Turbo Audi RS4, and then the blown M3, and there was no contenst. At all.

Get the M3, you won't regret it.