Its unfortunete that you only get the X5 35d in the US to compare to Cayenne, when the X5 40d actually gets better miles per gal.

I have had the X5 30d, X5 35d & now the 50d, all my X5's have had the same options, but the 50d gets much better economy than the 35d. My average of 80% city driving & 20% country gives me 9.4ltr/100klm, and l am not a light footed driver.

The Cayenne here has an option of a offroad pack as well.

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