With 3 years of RVing on these tires it sounds like you have found your sweet spot already unless tires are experiencing uneven wear. Obviously, your tires are overkill for your rig but that is a good thing in the long run. ST tires are not exactly built like LT or P tires, they tend to run and provide better performance when aired up closer to max psi as stated on sidewall.
ST tires we have had on our TTs/5ers I would make sure they had enough weight capacity to cover rig's entire GVWR, then filled them to within 10#-15# of max psi that way sidewall flex is minimal. Under-inflated ST tires will build up a lot of heat which does weaken sidewall and can eventually lead to premature tire failure resulting in tread separation or worse, a blowout while underway.