Umm, I just drove the Z06, not half an hour ago..
It's a monster, a bit unnerving on the road although its looooads of fun with all that torque. Might want to go drive one before you make that choice, specially if youre going to be driving the car everyday. The Z is loud and uncomfortable but man is it fast. The M is quiet and comfortable, but nowhere as dangerous.
If it's raw speed you're after, get the Z. If you want everything else, get the M.