Margaret, I get why you are asking all these questions and such and there is nothing wrong with wanting to learn and know all that you can when it comes to such matters as this... :)
With all the marketing hype that has been going on with all makes and models of vehicles for the past 10+ years, everyone has gotten ultra sensitive to the limits and ratings and such.
What you have to determine for YOURSELF is what do you feel the most comfortable with in terms of the "tow ratings", "payload", "hitch weight", etc in terms of exceeding or NOT exceeding any one or all of them??
Everyone that has posted to all your questions have their own idea of what limits work for them and tell you so.. What gets these posts going is the banter back and forth between everyone that has different opinions on the subject..
You've read all the different replies, so I'll not rehash them here, so you have all the info we can give you based on our own opinions and what WE are individually comfortable with doing with our own combos and safety factors.
You've got some miles under your belt with your current combo... So, how did it do with your butts in the seat?? Did the driver have white knuckles the whole way? Did the driver say it was okay? Bottom line, would the driver want to tow that combo again?
Depending on those answers and how you truly feel about the actual weight numbers is up to YOU.. :)
Being "safe" on the highway is a very speculative term IMO... I mean, if I was driving next to a "seasoned" RVer that was a tad overweight on his rig, but has towed for many years and thousands of miles, I'd feel a heck of a lot more comfortable in that situation than I would driving next to an inexperienced RVer towing for the first or even with very little seat time and towing UNDER all of his weight ratings... ;)
Of course, you don't know any of this following or passing, or being passed by either driver, but the point is there is a lot more to towing than just the numbers... It's how confident and what the driver knows about his rig that counts most..
I wish you the best of luck and hope you are able to enjoy this thing we call RVing.. :)
Mitch