I ran 16 PSI on the rears of my AWD, and 22 on the fronts. My axles are all RAXLES, so they're pretty beefy.

Start with 18 PSI and see how it goes. Lower the tire pressure 1 PSI each time until you get to the verge of tire shake, then bump it up a pound or two.

You bought these tires to hook, right? Why baby them because of an axle? Chances are if they break, you probably needed to replace them anyway. Drive it like you stole it or else you won't be getting your investment out of those tires.