You need a 4.8is. I have a 2002 M Roadster with the S54 engine and it's great. But, I think that the X5 is as much fun to drive (at least the 4.8). I think that the 3.0 engine is not powerfoul enough for a 5Klb vehicle.

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2005 X5 4.8is/ Imola Red/ Cream
2002 ///M Roadster/ Alpine White/ Imola Red (SOLD!)
2008 ///M5 ordered and on it's way!!