I have both an X5M and E92 M3, both are great cars and both have their advantages and disadvantages over the other. The X5M is super fast and has a lot of room for me, bring that I'm 6'6" tall. So, the wife drives the M3 and I drive the X5M, and I have an E39 M5 for weekend fun and track events.
If I had to pick one over the other, I would pick the X5M. Plus the X5M is faster!!!
///X5M...tracking a VIR....more so a parade lap with the BMWCCA Tarheel Chapter this past July.