Well I have been working and driving all of them. My lead BMW tech drives a 93 850 and my 97 540 makes it look like a diesel.
If you autocross maybe there is merit to a six speed. Unless you like to look childish I'll take you to the next light every time in my 5HP30. If what you really want to do is drive to Ocala to the Thai restraunt with your daughter and her corvette driving husband at 90mph with a little lite music and conversation while dodging all the rice burners going a hundred or more the 540 has no comparison. And of course if the need for speed erupts (to hit that hole) ain't none of them gonna touch her.
We work on MB to BMWs two to one, as thats our market and my expertise. I guarantee we do more overheating problems on BMWs. Having gone through my senior year of college with a XKE that always overheated and then getting thrown all the overheating Vegas as a dealer chevy tech, I was really glad when I got to MB; a car that has no inherent overheating problems, even in Florida!
But, to each his own.
Bosch Master, ASE Master, L1
33 years MB technician