I test drove an X5M yesterday at a dealer, it's an amazing beast, but at about only 10 mpg (if you drive it like an M car should be driven) the cost of ownership would not be fun.
After the test drive I asked to test drive an X5 35d, and I gotta tell you I was damm impressed with the power and torque on it, and this is coming right after testing an X5M. Honestly, I thought just stock the X5 35d had great torque!
Now if only BMWNA would bring the X5 M50d to the States, I think I would have my perfect car - M power and performance coupled with diesel gas mileage
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