I'm against mixing tires in any case. And on a car that focuses on handling it's even less desirable. And if you're doing it for a track event it's an especially poor idea.
If you're mixing tires on the Corolla you commute to work in, it's not ideal but I can see why someone might do it. In an M3? On the track?? No.
I have accepted a new position at Tire Rack and am no longer in the sales department. firstname.lastname@example.org
is available to assist with M3 questions.