i've broken 2 d30 r&p's with 33's. niether was being stressed at the time but from previous damage. you can't predict shock loads applied to the front end by bouncing your front end off of an obstacle. one overly aggressive pedal smash to overcome an obstacle can take out any drivetrain component. the guys running 37's on d30's probably wheel in very smooth and predictable terrain. or they know their rig well enough to know where the limit is. plenty of truck guys run 44" tires on 1/2 ton axles on the steet. 44's on 1/2 tons doesn't work offroad in most situations. i'm running 37's on a dana 44 front and i'm very careful.

i ran 35's on an amc 20(which is widely considered a crappy rear axle) for years without problems. i think i just got lucky. there are a lot of toyota guys here in az running 40's on toy 8" axles. they make it work but many are upgrading to 1 tons. there must be a reason. running anything bigger than 33's in hard terrain with a d30 is rolling the dice imo.