I don't think that they do get better mileage. The E70 has some more technology, but is heavier. Driving style makes more difference than anything else.

The US government fuel consumption test was changed, so the published numbers are different. You can't compare published figures for different years of vehicles any longer, unless you read a chart that has the different tests listed side by side. In theory, published figures should be worse for 2008, but there are so many adjustment factors included in the published number that it is a bit of a joke.

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2007 X3 3.0si, 6 MT, Premium, White

Retired:
2008 535i, 6 MT, M Sport, Premium, Space Grey
2003 X5 3.0 Steptronic, Premium, Titanium Silver
2002 325xi 5 MT, Steel Grey
2004 Z4 3.0 Premium, Sport, SMG, Maldives Blue