Originally Posted by Protocav
Start by adding a 5mm spacer to the rear. If you get wider rear tires, you will just induce push with the front. It will solve the throttle oversteer, but you will probably loose the crispness on turn-in. It sounds like the car is well balanced but just needs a tiny bit of rear grip. Try lowering your rear tire pressure 1-2 psi as well.
Some might say to be more patient on exit, but we all know that isn't fun at all
Oversteer is way more fun than understeer! I don't track my M3 much so I haven't played with pressures yet. I just notice that I have to be a lot more mindful of what my rear end is doing
in the M3 vs the 330. The 330 behaves much better.