I helped a buddy do a differential swap on his Jeep years ago - I remember we installed Detroit Lockers on both the front and rear with 4.10 ratio gears in both. However, that was on a manual transfer case vehicle with none of the sophisticated systems on an X5.

The guy who can answer your question is Brett Anderson of Koala Motorsports (www.http://www.koalamotorsport.com). Brett is a technical advisor for the BMWCCA Roundel magazine. Koala Motorsports sells Quaife racing differentials for different BMW models, so it's likely that Brett would have the definitive answer. If you find out, post the answer. It would be good information to have.

Regards, Mike