35s with cromos and staying smart with the skinny pedal works well.
If you have a heavy foot and you like hard trails, anything larger than 31s-32s and you're looking at axle carnage at some point
That being said, lots and lots of people use their Jeeps on the hardest trails in Moab, or go through Rubicon couple times a year turning 35s on D30/ 8.25 or D44 rears without issues. It's all about your driving style, but the limits of the fairly small R&P and the generally weakish design of the D30 causes gear deflection (and breakage) at some point. Trussing it and using a HD diff cover makes the HP D30 a lot stronger.
1998 Grand Cherokee 5.9 LX daily driver, 1.75" BB, 32" KM2s, HPD30 Eaton e-locker/D44a stock LSD, 4.56 gears, custom- fabbed tube bumpers and tube fenders,...
1990 XJ Limited (4-door), 4.0 I6, AW4, NP242, ***rolled and totalled @ 165k miles***
1990 XJ (4-door), 4.0 I6, AW4, NP242, PBR 42" tires, Unimog 404 portal axles, 110" WB, full cage + uniframe completely rebuilt, front 3-link + panhard / double triangulated 4-link rear,... ***SOLD***