ive had a 4.4 (06) and now a 4.8is and the 4.8 makes the 4.4 seem slow. plus, youre driving a rare beast with a 4.8.
drive them back to back if you can. that's what i did and it sold me on the 4.8

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01 X5 3.0i (gone)
04 X5 4.8is (gone)
06 X5 4.4i (gone)
09 X5 35d (current)
12 X5 35d (current)