Did exactly the same thing, replaced 07 X5 4.8 with 5.0i.
I live at over 9600ft, and I have to say the difference between the 4.8 V8 and the 4.4 V8 Twin turbo is astounding. A huge difference in power and acceleration. It must be more apparent due to so much power being robbed at altitude from the normally aspirated 4.8 V8. The 4.4 V8 Twin Turbo is simply the best engine I have ever had in a car.
The sound of the 4.4 Twin Turbo is also fantastic.
The steering feels slightly heavier that the old car when parking (I did not have the active steering on either car). Not a big deal and I only noticed it immediately after handing in my old car. The handling is much more refined ( I had the adaptive drive on both) both with 19inch winter rims or 20" summer rims.
I got the nappa leather and comfort seats, would never go back.
The eight speed tranny is also a significant improvement to the driving experience, it is super slick, almost feels like you are in an F1 car how quickly it slips up and down the range.

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2011 X5 5.0i, Sparkling Bronze, Premium, Sport, Technology, Winter, Premium Sound, Comfort Access,Heated Rear Seats, Rear Climate, Running Boards, Smartphone/Bluetooth package, 20" wheels