What to watch for when inspecting X5 4.4i

[FlytoFish]

Hello everyone! As you can tell from the number of posts, I'm extremely new here. My wife and I are considering trading in our 2005 VW Golf TDI for something a little larger and are considering the X5.

I currently own a 96 M3, just picked it up about two months ago and I can't seem to wipe the smile off my face every time I drive it.

I'm a fairly competent mechanic and generally there's nothing that I can't do, with the right tools and manual. When doing a pre-purchase inspection on my M3, I think that I scared the PO with the thoroughness of my inspection. His buddy used to be a BMW mechanic and he was actually impressed with what I looked at and looked for.

At any rate, not knowing anything about the X5's, I'm just curious on what things should be looked at as potential problems. I know the motor is one thing that needs to be inspected, and I do have a compression tester and know how to do the test, but what compression numbers should I be looking for?
Any other areas that are of particular concern?

Any information would be greatly appreciated. Also, what kind of economy can I expect between the 4.4 and the 3.0? Obviously fuel is extremely cheap right now, but I know it's going to be going up, so economy is a little on the back of my mind.

Thanks everyone!