Lots of great advice. Gas mileage is the same for either and both use premium fuel. The 2006 uses later technology which you might or might not like better. It would be an easier decision if the 4.4 had 15,000 less miles even if you paid a few thousand more. That said, at 75,000 miles you could have another 25,000-30,000 or more miles before you are spending to rebuild wear items like suspension, etc. Would be great if you could find out the history of the vehicle. Used BMW prices in this area have been steadily declining in this area. I expect KBB hasn't kept up. Independent dealers usually don't have to be pressed hard to sweeten the deal with new tires. Might be a negotiation item against any problems with PPI. Sounds like you are ready to upgrade if all goes well with PPI-----good luck either way.

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