Keep in mind that you have a couple of different factors in play.
I'm all for higher air pressure, lower rolling resistance, less chance of rim pinches, etc. BUT, the S-2 Rims were NOT designed to run 65 PSI. That's three times the original design tire air pressure. I have seen 2.125 Schwinn balloon Cruiser wheels come into the bike shop with over inflation and the sides of the rim were deformed and angled out. The tire had not yet blown, and it was still holding the extreme air pressure. I have no idea what kind of air pressure it took to deform the rim, I just let it out ASAP.
Even if the newer tire materials will hold higher air pressure, you're still using the OLD rims. If you want, or need to run 65 PSI, you're going to need to run a modern rim that is designed to hold the higher air pressure.
IMO, if you can stay at 50 psi or lower, and you have vintage rims without any rust damage inside, you should be safe.
John