As far as I know, the axle size does play into it, not just from a breaking axle shafts point of view, but the actual size of the housing and the bearings being able to carry the extra weight. The towing capacity will also change with your ring and pinion, but I think the ultimate limiting factor is the weight of the vehicle.. And maybe the brakes..
And I know you know this, but I'll say it for anyone who might not know;
It doesn't really matter if you have 400hp and "can" pull 10,000 pounds, it's being able to control it once it's going that puts a rating on things.. When you put a bunch of tongue load on your rig without a weight distributing hitch, it takes all the traction off the front end and you have terrible braking and steering... Very dangerous.
05 Tj, long arm, one ton, lockers, winches, 39.5" Iroks