With those choices, it's got to be the X5d. I also test drove the Q5 and really liked the car like feel and sporty acceleration. But the longer I sat in it, the more cramped I felt. I'm 6' 1" and it really felt small inside to me. That's especially true when you try and squeeze under the rear hatch, which will be a constant strain for your size.

As far as mpg is concerned on the 35i, I get a combined 19mpg, with mostly urban drivin and I have a heavy foot. I would expect to get 22mpg with the Diesel.