I had a M3 E36 & my 3dr both at the same time for 2 yrs, the M3 is a far superior car, handling on a M3 is better & you don't have to do anything to the suspension. A proper stage 1 cossie would keep up with a M3 no probs but if i was sitting at 155mph i would rather be in the M3 than my cossie as i know its not going to go bang at that speed.
Saying all that though cossies are by far more fun to drive than M3's
It doesn't matter what cars you have,if youv'e had a cossie you always come back to them again after saying you wouldn't have another because its a wallet breaker
Simon.