I like to stay between 65 and 70...closer to 65. I have caught myself doing 75 a time or two on a really smooth, no traffic road. But here in Michigan (the orange barrel state), I notice going over 65 usually makes the tt sway a bit, and I don't like that!
I hate to admit this but I just get in and drive. Have a GMC Denali Sierra one ton pulling a 346Qbud 40ft. fiver. Same tires on trailer as when we bought it, same for truck. We'll be doing tires before the winter migration. We went east cost 95 down to Florida and picked up I10 across to CA. Came back on I80 after a great visit around San Francisco and running up and down the west coast to view the Pacific Ocean. Saying all this so you understand I sometimes forget and catch myself doing 80mph. As when we were going over Donner Pass. No one could be more surprised that than me that I was able to keep the whole rig on the road. We had no problems and Lord knows I was blessed to escape with no problems. Just saying I think sometimes it's just dumb luck on how things go; not good planning. I always plan to not go over 65mph but I have caught myself many times edging up on 80mph. Stay safe out there!