I started on the ORC yota list in about 97 or 98 (well b4 Geiger took over as mod). From long term observation I have concluded that front axle Birfield life is determined by tire size, tire width, axle ratio, front locker, and transfer ratio. No surprises there!
Along the way I formulated some RoT's. These have been fine tuned from repeated observation of damage posts.
If you go over 33", eventually you're going to have trouble.
If you go over 10.50", eventually you're going to have trouble.
If you go lower than what puts you back to stock shift points, or to 5.29's, eventually you're going to have trouble.
If you have a front locker, eventually you're going to have trouble.
If you have any sort of aftermarket transfer case gearset, eventually you're going to have trouble.
Adding any two or more of these factors together just about guarantees a broken Birfield. Carry a spare or two and the tools needed for replacement.
Keep in mind that these RoT's apply to hard core off roading and were formed b4 the common availability of aftermarket, higher strength Birfields.