There are 2 failure points on the D30 axle. The first is the smaller 260 U-joint (the D44's use a 297, about 30% stronger), the second is the 7.125" ring gear (d44's use an 8.5" ring gear).
Upgrading to the warn shafts will, I have heard, get you to the larger U-joints, but the smaller ring gear remains. I have heard you can have it cryo'ed to add some strength, but I don't know the amount of strength or the cost.
The shafts themselves never fail, or at least I have never heard of them failing, and I have seen a lot of toasted D30's. The D30 uses a 1.13" 27 spline shaft, whereas the D44 uses a 1.31" 30 spline shafts, considerably larger and more splines.
You could upgrade the shafts, but then you might strip the teeth off the ring gear like an ear of corn (see picture), which is even worse. This guy was running 34" Swampers behind a T-176 with the 258. Yes, he wheels it hard and you can see the Lockright, but I'd still hate to have it happen. No rock around here, it's the dirt hills with ocasional rocks thrown in for good measure that breaks everything, or the mud in the spring.
I'd swap to a D44 if the cost were about the same. Outboarding the springs is easy, cheap, and removeable (at least my writeup is), but having a shaft cut down shouldn't be a TON of money, it should be around $350 extra at the most.
This is one I saw last night, it's a D30 with chewed spider gears. I had to get a pic. There is something to be said for SIZE.
Winter Harbor, Maine
'81 CJ-8 Scrambled, It's a Jeep, Chevy, IHC kinda thing!
'88.5 Zuki, 7" Lift, Locked, Swamped, Rolled, and just generally broken in right!