sat in the new 650i at the dealer yesterrday.
it really is amazing. the seating position is even better/more comfortable than the m5. certain things look a little better thought out than the m5, like the cup holder lid slides open and closed much more fluid like. instead of the kindof cheap feel it has when pressing it on the m5. (sometimes i have to smack that thing to get it open) the same with the little swing open storage compartment on the center console, much nicer gliding action. the paddle shifters are in REAL brushed aluminum.
certain things seemed off though, like; even though the dash was leather (nicer, softer leather than the leather on the m5) - certain other parts that are leather on the m5 are in "cheapy" vinyl on the 650i, like the glove compartment, area around the center stack, and lower panels on the doors...
maybe the m6 has the FULL leather treatement.
otherwise, amazing. demolishes ANYTHING by mercedes, IMO. including the SLS.