I don't think I can detect any real difference. Here's a test: have a passenger randomly select the Sport/non-Sport button while driving and see if you can determine which setting is selected. Try it about ten times. (you might have to put some tape over the dash indicator light).

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