depends on amount if sticky pedal and presence of lockers.
That said mud isnt nearly as hard on em as rocks. (well at least not on the shafts....bearinss and such will be ruined in mud but more beef wont eliminate that problem)
I did pretty well for a few years with 35's in my burb. When I went to 15.50/33's axles started to break too often. Usually it was when wheel went air born under power. Tire slippage is easier on axles.