I got to drive both a 2009 E90 this morning and a 2009 GT500 ( in the rainy weather so it was a little frustrating). In summary, the M is just hands down the better car overall. The steering feel was much better, the interior much nicer, it felt much lighter (which surprised me as i thought both cars were in the same heavy weight range). The one thing is that the GT500 looks absolutely unbelievable. I had never gotten to see one up close like this, and I have to say that it blew me away.
Overall I'm heavily leaning towards the M3 at this point but I'll give myself a few more days to think before I make a move.
Thanks for all of the good advice!