I drove both at the M performance driving school, and I was very very impressed with the M5 and not so much with the M6. Maybe it's because I had better expectations with the M6.
The M5 handeled just as well and the power of course was the same.
It's an awesome car!
http://www.e90post.com/forums/showth...driving+school
My vote--M5 all the way!