I have an '01 X5 3.0 and an '07 4.8. The 4.8 is deffinatly a rocket but I've never been bothered by a lack of power from the 3.0. In '01 the 3.0 was only 225 hp, but it still had a lot of get up and go. I guess if you put your foot into it a lot you'd like the 4.8 way better, but for ordinary driving around the 3.0 is plenty. I love both of these cars for their handling, looks, and just that BMW feel.

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2007 X5 4.8i Space Gray
2001 X5 3.0 Titanium Silver