A well maintained, lower mileage and documented 3.0 or 4.4 vehicles that passes a stringent PPI would be at the top of my list. All things being equal other than price--consider the lower price vehicle as having a 'bank account' for potential future issues. If you intend to keep the vehicle a fairly long time it is important you try to learn how to take care of any future problems yourself or to can quickly become a bad investment. Assuming you find a 3.0 that passes the criteria, even though logic says the 3.0 is a wiser investment, it is really an educated guess.

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X5 4.6 2002 Black Sap, Black interior. 2013 X5M Melbourne Red, Bamboo interior
Dallas