I average 13.5 around town. If I drive any highway, e.g. mall/downtown that goes up to 15+. Have not taken any long trips (mostly highway) yet.

The X5 has plenty of power to speed up or pass. The performance is fine and I'm comparing 0-60 mph times of the X5 (6.1 secs) to a C32 (4.6 secs). No hard data but I'm guessing that 6.1 seconds is 90% faster than most cars out on the road.