Ya dude, remember the Rubicon Tj's can clear the Rubicon trail and they're only on 31's, you'll only gain 1inch of clearance per 2 inches of tire diameter increase. And that add's a LOT of weight. If you're looking to get through the Rubicon or some of the Moab trails than I'd just go w/d44's with really deep gears and 33's with a big lift.
I drove the Rubicon on 31s, w/a one inch shackle lift, stock axles and an aussie in the front, stock gears, stock transfer-case gearing, and a lot of new armor. I was banging rocks the whole way for 12+ miles; I was also driving probably the easiest lines the trail had.
The crazy thing was on that trip, except for the end of the second day on the trail where we were able to get with a group of big TJs and built pickups for about a half-hour on the downhill to Rubicon Springs, we -- my Dad and I -- ended up running the Rubicon in a solo jeep. That's wasn't in the plans -- I figured end of summer, there'd be a ton of people there and lots of groups to get with from start to finish. Didn't happen.
Anyway, my guess is 33s or 35s would have given a lot more leeway in terms of line-selection and made the run a little less work. But, it was doable on 31s... If you've got a group to go with, then maybe get yourself at least some 33s and a 4 inch lift and then you can enjoy yourself.
