I have owned both 35d and 35i. I like the gas N55 a LOT more. A big thing for me is that there is no vibration while idling at a stoplight. I was tired of the diesel vibration. The gas engine has a sexy sound and the mileage is just about the same on the highway. I would say it is about 1/2 mpg less on hwy and 1-2 mpg less around town than the diesel 6 speed.

I will get a gas engine with next X5 also because Illinois sells only B20 biodiesel.

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Whalerdude