I just can't see driving an RV at 65-75. It's not a sports car.
From San Antonio to El Paso interstate 10 is 550 miles of extremely smooth, well designed divided highway with speed limits of 80 mph for much of the way. There is almost nothing of interest between those two points, esp. if your trip objective is somewhere west.
You'd be insane to not run at the maximum safe speed of your vehicle.
Many RV trailer tires are only rated to 65 mph, although there are some 80 mph rated ones becoming common because people are so tempted to gain back those extra hours of travel time slowing to 65 involves.
The maximum safe speed varies according to conditions, of course, but it is the actual maximum safe speed. By definition you can drive at maximum safe speed all day long with only the usually accepted risk of vehicular travel.
I've driven at high speeds, too, but only in a car with tires rated for high speed. I have an old Ford truck, and I never drive it over 60.
If you're going to drive fast, it's your responsibility to ensure your vehicle is in shape for it, with tires and brakes are in excellent condition and properly rated for the conditions.
I mentioned earlier that I was getting my hangar queen back on the road, and without question that means the brake system / suspension is getting thoroughly overhauled, and brand new tires. (Tires can look brand new, but they age and deteriorate and get unsafe.)
You don't need sports-car maneuverability on big, fairly light-traffic interstates.