Go for the Diesel.

Same situation I was in a few month ago.

Diesel was my favorite from the beginning.

We went and test drove both.
First the Diesel and I did not even drove shotgun on the gas X5.
She came back 3 minutes later and said "This thing wont move at all".
the 2011 Diesel it was. I need to say that was a non turbo 2010 3l gas she drove.

The torque makes a huge difference and since you fill the gas, you will be happy to be able to get 500 miles out of one tank.