I seem to be getting slightly better gas mileage in my 2005 X3 (17-25) than in my Mother's 2002 X5, which was running around 15-22 mpg. As I understand it, these have the same 3.0 L I6, so I have got to assume that the difference could be attributed to weight and, likely, the extra gear in the X3. Both are manual transmission vehicles, but hers is a 5spd.

Size-wise, they really do not look very different, but they definitely feel different. While the X5 lacks for nothing in the get up and go category compared with the X3, I definitely noticed it's largeness in parking and negotiation a crowded (offroad-ish) campsite.

FWIW: The more I drove the X5, the smaller it seemed to me. Same thing is happening with the X3 (have about 400 miles on her since I got her last week), so everything is proportional I guess.

Good luck,
D