If you still have the D30 front and D35 rear, then I'd be worried. Dry rocks have a lot of traction, and tall tires increase the leverage on the axle shaft. If I was you, I'd find a spare rear axle shaft, and bring it with me for a spare. ALL of the shafts are weak. So are both ring and pinions. So are lunchbox lockers. However, the rear alxe breaking can cause the tire to 'walk' out from under the YJ due to the C-clip design. That can be a PITA. By carrying a spare shaft, you can at least have tires under the jeep.
And as a side note, the phrase; "are these tires too big?" is one of the wheelin' questions that never has a valid answer. It's like asking; "are these boobs too big?". Some guys like 'em small, some guys like 'em big, some guys like 'em ginormous. Pesonally, I like 'em all.