What did the 4.5" lift come with? That is alot of lift if you plan on keeping you stock length lower control arms, your ride is going to suffer considerably and rough country coils are pretty stiff.
I ran a 4.5" lift on my Comanche, which is the same as your XJ from the doors forward, and ran 32x11.5 tires and they rubbed on the unibody on the upper coil spring mount, and they rubbed the lower control arms like crazy, and the welded pinch seam on the back of the wheel well. I got my bumpstops adjusted properly and got rid of the rubbing on the unibody, and then pounded the pinch seam over flat. But with stock rims you will rub on the lower control arms even with 31" tires, you need a bit more backspacing or adjust your steering stops so you cant turn as sharp (its not much and you don't really loose any steering its such a small amount). I was even able to run 33x12.5's after some minor trimming.
31's might look small on 4.5" of lift, I think I would go 32"s and really fine tune your bump stops, and fold that pinch seam over. But thats me and I don't mind a bit of trimming, I'd rather do some tasteful trimming then add more lift.
If you want alot more information check out:
http://www.naxja.org/forum/ and
http://www.jeepsunlimited.com/forums/forumdisplay.php?f=19
