I'd go from my 4.8 into a 35d or 35i anyday. Though I picked the 35i simply because I like the new M-Sport kit a lot. And I'm hoping that they 8-speed will make the car more enjoyable and smooth to drive (for daily driving). Of course, all this would be subject to actually test driving the 35i to truly compare and make a good decision.

It also depends on how you drive and intend to drive the car.

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2008 X5 4.8
White w/ Black Interior w/ Bamboo Trim | Premium | Sports + 214" | Tech | Cold Weather | Rear Climate | Premium Sound | Active Vent Seats | Heads-Up | Comfort Access | 3rd Row | Aero Kit | Huper Optik Tint | Clear Reflectors