If that's the case, then why does the tire say 65# max at max load?

The OP is moving with a loaded vehicle, over pressure sure is better than under pressure that's for sure on the highway. I wonder what he has been running up until now? If the tire says 65#, then why would you be afraid to run 65#?

I have trailered over 250K miles in the last 25 years with my trailer tires over filled by 10# from what the sidewall says on 5 different trailers and no tire trouble. I have wore out many trailer tires and none have failed, my experience. Only trailer tires should be over filled if you are going to drive 65MPH+ on the highway.

I stand by what I recommended as I maintain many vehicles for a living not all driven by me. And I would run the same pressure in all tires.