Ok, I've got it. On page 88 of the BMW Car magazine September issue, you can find specs of all the X5's. It shows that the 286hp 4.4 (pre 2004) does 0-62mph in 7.5 secs while the 320hp 4.4 (post 2004) does 0-62mph in 7 seconds.

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2008 Saphire Black on Biege.