It may be of use to know that the current X5 3.0D can give up to 35mpg on freeway and about 27 around town. Engine size is 2996cm3 with similar torque to the 4.8, but being a diesel runs out of revs earlier of course. 218bhp according to the book and under 9 secs 0-62mph.

These are the figures I get from my 2005 3.0D Sport Auto. The next generation engines may be even more efficient as Europe also tightens the emissions regulations further to require EU 5 performance. The current version is EU 3.

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Me:
Current: 2011 E71 40D Vermilion Red/Beige Nappa

Wifey:
Current: 2012 R80 Countryman SDX Green/Cream