This is enough of a difference to make me want to find a cheap 5 speed XJ (Jeep Cherokee) as a city beater/DD. The ability to EOC, etc, and the 1100 pound weight reduction over my current Jeep would make a huge difference. I'd probably be getting 16 - 18 city, versus my current 12 - 13. On the highway, the difference would be mostly due to the smaller engine.
Unfortunately, this and/or a manual tranny swap in my Jeep will likely have to wait until after college, due to budget, and nowhere to store 2 vehicles up here, amongst other things.
If I could find a place to store the 5.9, I'd keep the XJ on campus, and the 5.9 elsewhere, and use it to trailer the XJ up here and back home. The roads around here would be great for EOC. However, the reduction in space for stuff, and the much less comfortable ride is enough that I wouldn't want to just drive the XJ up here and have it as my only vehicle during college.
Or, maybe I'd even get a smaller manual tranny vehicle, but my biggest limitation is that I HATE FWD, and small, efficient RWD vehicles are hard to come by...