i've had both, and both got about the same fuel economy for me. i read somewhere on here about how the increased power of the 4.0 offsets the decreased fuel consumption of the 2.5, so it ends up being a wash. so if it's a decision between the two, i'd recommend going the 4.0 route. after struggling behind the 2.5, i feel like i can tow the world with it
1996 XJ Country, 4.0, aw-4, 2wd :(
1995 XJ SE, 2.5, ax-5, 231, cancerous unibod...traded^
1995 XJ Country, 4.0, aw-4, 231, babysat for brother...