I thought the GT 5 would be a nice blend of performance and function. The sales manager suggested I drive the X5M. The X5M was much more fun to drive and more functional. Surprisingly comfortable than the GT with a more supple ride. The ride is tons better than a standard X5. The M's handling rivals virtually any sport sedan. It is big and heavy and the mileage is atrocious - but expected. Don't have enough miles to judge reliability.
Acceleration and handling.
New IDrive is better than before but could use further simplification.