We would need to know the options, price, etc on the ones you are looking at. The main 2 differences between '09 and '10 is the '10 Sports Pack does not have Adaptive Drive standard (it is a stand alone option only) and the '10 has the newer iDrive.

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2008 X5 4.8
Jet Black/Black Nevada/Dark Burl Walnut
Adaptive Drive
Premium Pack
Tech Pack
Climate Pack
Sport Pack
20" Wheel Option
Premium Sound
Sirius Satellite
Rear DVD Entertainment
Multi-Contour Seats
Comfort Access
3rd Row Seat
Heated Front Seats
Running Boards
3M VentureShield Paint Protection Film