Hey, welcome to the DARK SIDE!
Great group over here, ask anything you'd like.
Why 31x11.5? The common size is 31x10.5, and they fit without any lift at all, we have been running them for 5 years and about 90,000 miles (original 30" tires were ripped off and thrown away at 15,000 miles).
We got the ABS with ours (works awesome, but seems to not work off-road at slow speeds, which is good) and cannot modify our TJ's suspension due to state regs. We have wheeled it hard with the 31's on it, and quite frankly I've been amazed at where it'd go. Add a set of front disconnects, some tow hooks (not sure of what the "X" package is), take the doors off, and wheel it to your liking.
We have had it back a few times for warranty work (rear axle, header, radiator, Cat, exhaust, TPI, radio), and they looked at it funny but never gave us a hassle with the 31's. The top side looks mint (until a few years ago), but the underside looks like you took a sledgehammer to it, all the bolts are rounded off.
Here are a few pics. The interior is pretty well protected against water, but the cassette isn't. The soft doors in the pic are converted CJ soft doors I picked up on Ebay for $65.
JEEPN
Waldoboro, Maine (yes, we're BACK!)
'81 CJ-8 Scrambled, It's a Jeep, Chevy, IHC kinda thing!
'88.5 Slamurai, 7" Lift, Locked, Swamped, Rolled, and just generally broken in right!