Don't bother with the M. The catastrophe you will have in reliability is just not worth it and the 5.0 is ridiculously effective. 3 stop lights in a row a Lambo couldn't leave me. AWD and torque are awesome. I am a HUGE M fan, but these days the possibility of ridiculous repair bills make them unobtanium. Damn AMG taught me that.
...of course I still really NEED an S8.