The rear wheel drive only conversion would be awesome. But if you live in an area like northern Utah where you see snow 5 months out of the year, the awd system comes in handy.

Not sure what sensors are involved in disabling the the front drive train but can be done. The awd system most likely looks for a certain set of conditions so it would be hard to trick the ecu as I did on my e36 manual conversion. The automatic trans ecu is still intact and the vehicle operates perfectly like factory with cruise control and all. In the case of the X5, a reflash of the ecu would be needed (540i for example). I may make a phone call and talk with Mr. Conforti himself about that. (shark injector and monotronics expert.) You would see improved economy without the parasitic drag of the front drive line.

As far as the 6 speed conversion, looks like I will need a few specific parts. Trans mount brace, the correct section of drive shaft going to the rear as well as the shaft going from the transfer case to the front diff. due to increased length. As far as I can tell there were no changes made to the underside of the chassie of the e53 post facelift. So no worries about clearance fitment. I'll post as I learn more. Thanks for the replies.