I've had a fair bit of wheel time (a week in each) in an X6 35d and an X6 35i and the 35d has more real world grunt than the 35i even if the 35i has a smidge more top end. And 35i uses approx 30% more fuel. Don't get me wrong, the 35i is sweet as, but for day to day driving it can't match the instant get up and go of the 35d.