I have a 2.5" OME lift (DPG Ultimate Kit, haven't installed the 1.25" bl yet though) and I run 33x12.50 mtr's w/ kevlar. They fit fine and there is still room for some flex. As long as you run the correct bump stop length for your shocks it won't be a problem.
With that said, depending upon where you like to off-road makes a difference. I live in Mississippi so it's mostly flat land here with a bunch of mud holes so there isn't much flexing to worry about. But if I was gonna be running my jeep in Moab or rock crawling in general I would probably go with a 3.5" to 4" for 33's.