With that 5th wheel weight I would go with G-rated LT tires, not the E-rated. Just not enough carrying capacity IMO. That is, of course, if your wheels will handle the added pressure of 110 psi tires. If not, and you want to stay away from ST tires, you may have to look at different wheels and tires.
You say your 5th wheel weighs 11,500 lbs. on the two axles, which in an ideal world equals 5750 lbs. on each axle. However you may have less than that on one axle and more than that on another, perhaps 6300 lbs. on one axle and 5200 lbs. on the other axle. That would put you over your tire weight limit. Not an unlikely scenario.
I have a triple axle toyhauler and have a couple tires that have 1200 lbs. more than the other four. Not an issue as I have a lot of surplus carrying capacity.
Howard and Peggy
"Don't Panic"