Hmmm...still completely undecided. I may just wait for the better deal on either when I decide to buy. For plenty of reasons (I have almost no use of the rear seats/doors), the M3 is superior. I just wish it wasn't so damn common; I think the M5's rarity makes it more special. Also makes a better sound
Here's a short of the M5 (FF to 4:20 if you're impatient)