i have both a 4.8is and a 35d in my driveway. the 35d is a great car. torque is not instant like the V8 though. but it does come, and quite smoothly all the way through the power band. also, its shamefully quiet. like i said, a great car, very practical, real world fuel economy is fantastic (ours does mid 20s combined city/highway vs. the 4.8 which sits around 13). However, at the end of the day, its nowhere near as exciting to drive as the E53 4.8is it sits next to.
its tons of fun seeing your fuel range sit in the 500s. but i'll still hop in the 4.8 every time.

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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)