Oh and if you drive an M6 for a month, trust me, a 335 is not going to do much for you. The M3 is definitely a good option though. You will sacrifice some luxury for a bit more performance in the twisties. The M3 also seems to be more reliable.
For me the M6 is the perfect driving experience. It can transform from a comfortable cruiser to an absolute maniac. The scream of the V10 at 8,000 RPMS is just crazy!