You are not going to want to get anything bigger than 31 inches. With a 2" BB you could clear 32's with minimal rubbing. If you added 3" of lift (ie: 2" BB and a 1" Body Lift) you could clear 33" tires.
Some people might try to tell you that you could run 32-33" tires on stock suspension, while possible, you will be rubbing your flares like crazy with any flex in the suspension.
Don't forget that the Moab wheels have 5" of backspacing so you may need to add wheel spacers if you use a tire wider than 10.5". Hope this helps, you can also try a search for more answers.