Tell you what if I fit in an M3, I would probably go that way, but at 6'4" I am forced into the larger car. They are just two different animals. Having driven both, the current M3 is zippy, extremely responsive and amazing in the "tight twistys". Not having driven the new E60 M5, I only have experience with my E39 M5.It was stealthy, powerful, a bit heavy, but with just the right amount of under stear. I think it boils down to what you are personally looking for, quickness and sporty-ness in the M3, or power, luxury and blazing speed in the M5.