Just as a confirmation on the mileage on the 4.4, ours gets used around town a lot, and gets 12mpg doing so. It does not get driven too far on a day to day basis, so that's not too painful. But we do take trips with it, and it's an awsome road trip car. Drove it to Florida last month, with two on board and was getting 19mpg at ~75-80. Had another passeger and more luggage on the way back, and got 17mpg.

Drove it to NC, also last month, this time with 5 on board, and the car packed to capacity, and got 16mpg at 75-80. We had luggage literally packed to the roof.

I guess if you looked at highway mileage with just a driver, and no luggage, and stayed below 65, you might get 20mpg with a 4.4. But the whole point of an X5 is to be able to take a long trip with a crew of friends or family, with all their crap, and still cruise effortlessly at whatever speed you want.

I would drive both an I6 car and a V8 to see the difference. See what you prefer. Gas mileage and maintenence cost are definately factors, but then again, the V8 X5 is a completely awesome driving experience.

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2014 BMW 328i Xdrive
2011 BMW 335i M-Sport
2008 BMW X5 4.8i Sport
2000 BMW 528i 5sp