I'd go 35 spline. You're talking a low pinion rear axle with an 8.9" ring, a pinion diameter the same size as a Dana 60, and teeth angles that make for a very strong contact pattern. In fact, the max torque load is nearly the same as a high pinion Dana 60 (which is why it baffles me when someone buys a semi-float prorock 60).

I never thought twice about running 37s on that axle. With the tubes welded, I would even be fine with 40s - except the semi-float part of it would just fail.

Depending on tire size and how hard you wheel, I'd put more thought into the axle shafts. Even guys with the semi-float 60s and 37s are bending flanges with ease. Yeah, there are warranties, but it is still a pain in the a##. I'd get some RCVs and be done with it. And while you're there, upgrade to 300m.

 

I have seen people run 37s with the Jk non rubicon rears and 30 spline chromo shafts and run these hard but I know of at least one guy who had issue with the e locker and switched to ARB. Still running strong in rocks for more than a year now with 37 tires and H1 wheels

 

And H1 wheels with inner locks and military tires are easily 150 lbs per corner!