Awesome - congrats. Really nice vehicles and much better to drive than a X5 too. I had a 05 w/ manual and in retrospect wish I hadn't sold it. I had it 3 years and it was the best all around sedan I've owned, and just as fun to drive as a E39 M5 (yes, I had one of those too). Not quite as tossable as a E36 M3, but adding in the AWD factor for snow country driving and it was a very nice all-around sedan. In many ways I sure wish I still had mine!
Did you get an AT or stick? If manual, you may start thinking the M5 is redundant!
Here is a pic of my old steed:
Visit Audizine forum - not as good as Xoutpost, but not bad and a good source of info on these cars.
BTW - I sold my X5 this year too but not to upsize. We needed a larger family car so picked up a new Mazda CX9. I'm happy with it so far - just nudged past 7K miles on it after first half year of ownership.