Good subject here, with plenty of different opinions. I'll add my perspective. You do need to tell us what kind of wheeling you want to do, it makes a difference.
There is a little optimism with those who say they run 35's with 4.5" to 5.5" of lift. It can be done, and can be a very good way to go, but it will take A LOT of well thought out trimming. I run 35's with 8" of lift, I've trimmed quite a bit, and I still rub. How much you need to trim depends on how much flex you want to have......more flex means more trimming, less flex less trimming. There is no ideal condition here, it's what you want.
As far as gears, go with the 4.88's if you want to end up with 35's. I thought the 4.56's were good with 32's, with 33's I wished that I had 4.88's, so when I went to 35's I also went to 5.13 gears, which I think are perfect for my non-HO automatic. It's an old wives tale that 4.88's are weaker because of a smaller pinion.....Internet rumor with no basis in fact. The people who say it are repeating what they've heard or going by theory. Just as many people have broken 4.56's as have broken 4.88's, and few have broken either.
Regarding the D30 handling 35's, it can be done but it's going to cost you some coin. You'll need to, at minimum, run snap-ringed 760x axle joints, and stay out of the throttle. It is much preferable to run chromo axles, which have stronger splines and much stronger u-joint yokes. If the u-joint caps are snap-ringed or tack welded, the Spicer axle yokes will eventually fail by stretching and then breaking. The chromo axles won't stretch in the yokes, so the u-joint cross has to break to fail, which is less likely. You HAVE to snap ring them, or the c-clips will just pop off, the cap will walk out, and the cross will break. As an example, on a hardcore run we did last weekend with a dozen rigs, none of the guys with 35's and chromo axles had any breakage, on either D30's or D44's (both have the same axle joint), but there were six broken front axles on D30's with Spicer axles......all had snap ringed or welded caps, and all had 33's, and no one broke because of throttle.
As far as needing 35's, you don't. You will probably have more fun wheeling with 33's than with 35's because you'll break less. It makes little difference in trail performance, and virtually no difference in climbing ability. You can do some things easier with the 35's, but there is very little that you can do with 35's that you can't also do with 33's. I've been running hard trails with my XJ for 8 years, and I just went to 35's last year. In our group of rigs that regularly run some of the hardest trails around, many are still running 33's. Reliability is definitely an issue when you go to 35's, unless you do it mostly to be cool and stick to moderate trails. 35's are hard on steering as well as on the drivetrain, so you need to consider everything that will need to be upgraded.
Personally, I'd recommend going to the 33's. While you are wearing them out and gaining experience you can be adding upgrades to your rig, then when you need another set of tires go to the 35's. I can barely get a set of tires to last two years, so it's not that long a time. If you know you'll go to 35's eventually, go with the 4.88 gears....you'll never regret it.
