Thanks for the thoughts guys. I know I'm not the first to decide between these cars, but it's certainly a very difficult decision.
I think the one most different from my 335 and Boxster has to be the Z06, and I do start to smile in my head when I think of that exhaust and tremendous torque. But then, I go back to thinking about the sharpness of the M3 and ease to drive; and the nimbleness of the Cayman.
I think I will probably have to really drive each a few times to form a personal opinion.