If it was just a choice between engines, I'd easily get the diesel. But since you can't get the 4.8 sport look in the diesel (without going to a lot of post-delivery hassle and expense), it does give one pause to consider the 4.8i. It's not just the wheels - fender flares, exhaust tips, etc. Also, for some reason, you can't get active steering with the diesel engine. I like having active steering.

I second what mtech says about the 4.8i - it's not a very smooth delivery of power, very balky at times. My mileage isn't all that bad, but it's nowhere near the diesel mileage.

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2008 X5 4.8i, Jet Black, Tobacco Nevada leather & just about everything else (no vent. seats, no 3rd row)