I almost replaced my x5 with a 2008 535xi not long ago it is a heck of a car. My first thought is why not just buy a 2005 or newer x5. Personally I'd consider the newest nicest e53 I could afford to replace mine.

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2014 328xd
2015 f150 ecoboost
2002 x5 4.6is estoril blue
2003 x5 v8 sport
1996 F-250 diesel built not bought
2011 335d fbo tuned and deleted (now baby sisters racecar)
2001 x5 factory stickshift back of the barn, blown
2001 540i sport gone but still missed