I have a 96 2.5 XJ.
4.88's (don't even bother with 4.56's, the jump from the factory 4:10's just isn't worth the cash outlay)
31's
I travel 700 miles, all interstate all over the southeast and back home to the mtn's of NC every week for work. I get 17.5 - 18 mpg's. That's at a gps cert 68 mph...