I was looking into this too before I bought my first X5 a couple of weeks ago. Before this one I had a 4Runner.

One of my buds put 112k miles on his '03 4.4 without any problems, only regular maintenance. He traded it in for an '05.

Another friend racked up 166k miles on his '01 3.0, also with regular maintenance. He gave it to his dad when he bought a new one and it's still running perfectly.