The gas mileage between the two engines should not be a consideration in the purchase of an X5. If it is, you should probably look at another vehicle, as neither is frugal on fuel -- but not bad for an SUV. It is a no-brainer whether to get a 4.4 or a 3.0 if you have the money. If you must have a manual trany or if money is an issue, get a 3.0. If you can afford either, get the 4.4.