My Co-worker just got an X3m40 and I drove it. It's really fast and handles great especially for an SUV. The question is what are you looking for? A sporty car ride you can store a lot in or an more cushy SUV ride? The X5 seems more luxury orientated (more more sporty than other luxury sub's) and the x3 more sporty. I have a Z4 for sporty driving, looking something to feel like the sunny center of the universe while stuck in traffic.
And with a higher quality level.
I'm guessing Dinan will come out with a software update that will make it similar or higher hp than the X3m40.