I have a '99 540i/6 and I've been thinking about upgrading to the M5. I'm satisfied with the 540, but I think I would really love the M5. One thing that is holding me back is potential of BMW adding the SMG-2 transmission to the M5 over the next 2 or 3 years. If that is the case, then I can wait. My wife is still bugging me that she can't drive the 540!