Here is the thread on the X5 board where BMW sent letters saying the 4.6 was an M to new owners. You can contact the authors on that board if you need copies or anything. I think it is funny that the sales/marketing people at BMWNA are still calling the X5 4.6 and M. It must really have been designed to be an M. That much is obvious.
http://www.bimmer.org/x5/messages/ar...w01/82337.html