Overall, the X5M is an awesome vehicle. I owned a 2007 X5 4.8 previously and the X5M outperforms it in all categories. The layout of the X5 is basically the same for all E70 models but the ///M is decked out with "cooler" features (i.e. different gauges, paddle shifters, leather dash and of course, the 555hp engine!). If you are trying to decide on a new X5 50 or a used X5M, choose the X5M - it drives like a dream!
My wife had been driving a Lexus LX470, and the fuel cost was getting out of control. Nice car, but not economical to drive. We had rented diesels in europe and liked them, so we search one out back home. The BMW X5 Diesel has impressed from the test drive through today. The car was a lease return, and we had to have a minor fix done to it for maintenance that wasn't done right. But other than that, it is an absolute pleasure to drive - when I get a chance. It accelerates much stronger than the Lexus, handles like a finely tuned touring car, and milage has been 10 mpg better than the Lexus was getting city and highway. Third row seat are best for 10 year olds and under, and I wish it had a bit more cargo space. But for trips, this car is great. It does everything you ask it to do, and does it well. And we love stopping at the gas station half as often as we used to, and still have the power to pull away from most other SUVs.
This car looks great, is fun to drive, and is very comfortable on long trips. This is my first BMW and there are so many nice features on this car besides the things that are always advertised like navigation, sunroof, etc. There are a lot of little things that you don't get on less expensive cars like all 4 windows being 1-touch up and down, rain sensing wipers, lights under the door handles, and other cool features. The engine is super smooth and quiet even under full throttle. As for the interior, Mercedes is catching up in recent years, but for this model year BMW was light years ahead.