The tubes are more prone to twisting than actually bending, but I've seen a couple bend at the differential. It's a minority that will see this ever happen imo.
Much will depend on your driving style. If you like to 3-wheel and slam wheels to the ground, then any axle (and it's components) will be more subject to failure. If you avoid the skinny and wheel with finesse in most situations, then you should be okay. I feel that with a D30, that your real "weak-link" is your ring & pinion.....but again, a lot depends on your style of driving.
I wouldn't worry as much about the tubes as I would about the outer C's. These are much more prone to bending with 35"+ tires and the off-set of some aftermarket wheels. I would no matter what- gusset the C's, and if you are concerned then you can always add a sleeve kit and/or truss.
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