I'm gonna jump out there and contradict this entire thread. I have a 610 lbs ft flywheel motor in an 8.5 axle square body with a Trac loc and 295s. It has held up fine for 1500 miles. I drive the snot out of it. Are you all rock crawling with 35 inch tires? How are you breaking the 8.5 axle? What's the weak link? Street driving with a heavy foot and I've no issues. Even with a couple of burnouts with the 295 mt radials. I would expect an axle break rock crawling, but street strip? Why does everyone hate the 8.5? Granted it's not the famed Ford 9 inch or a 12 bolt, but it's got its place vs the Ford 8.8 and the notorious 7.5. Who broke an 8.5 and how?
I posted some torque ratings from performancetruck.net on the 10 bolt, 9.5" and 10.5" 14 bolts on a thread a while back. IIRC, the 10 bolt was rated at around 3600 lb-ft while the 9.5" was rated around 5,000 lb-ft. and 10.5 was around 6,500 lb-ft... numbers are numbers...I even did some basic math on engine TQ/axle ratio ratings on that thread...
I don't hate the 10 bolt, but have to accept it's one of the weak links in our 1500 trucks. Mine on my 1500 has made it to 260,000 miles under stock tires and a V6 with the G80/3.42s. I never really took the truck off road, but the few times I did, I was really careful I didn't go nuts on it (one time I was like 1,000 miles south of the US border, probably 20 kilometers from the nearest town, lol.)
For pavement only, it's fine. Throw some big tires AND a guy that likes to jab the gas, and you'll be rebuilding the thing in a matter of time...or the guys doing the crazy burnouts...or the guys with slicks at the track.
Admittedly, I think those are the guys blowing them up and NOT the guys just minding their business...then there's the G80/10 bolt "gov bomb" deal. I think the spider gears are prone to failure or the G80 in most those cases.