I just came from an X5 m-sport w/20" and all the options to an X3 m-sport 35i with all options because i wanted something a bit smaller and more economical. honestly, there is a difference in power (turbo 8 vs turbo 6) but the X3 feels way lighter and easier to maneuver, especially in tight spots like making a U turn. It is fun to drive and very quick. Not boring at all. the 300 hp turbo six has plenty of power for spirited driving. My X5 on the other hand was a handful. it felt heavy and the steering was a bit heavy too. This was easily overlooked when you mashed the pedal.
i honestly love the X3 and haven't looked back yet.