For approximately 0.7 secs slower 0-60 than the X3 M40i, you get luxury and performance in addition to the latest technologies and suspension options - 2-axle air, off-road package, laser lights, next gen. interior design.
I've considered and driven the X3 M40i - the performance is intoxicating but I'm in my X5 just under 2 hours, commuting 50+ miles a day. It's hard to give up the interior refinements and especially multi-contour seating just to zoom zoom faster.
Though the X3M/X4M might convince me otherwise
