I, too, have found that long journeys best break up into 300 mile ( More or less ) days. Counting the essential fuel, potty, food, and stretch-your-legs stops, that translates into 6-8 hours on the road. And if you fancy seeing some of the sights along the way, you might find it’s closer to 200 miles in that 8 hour day.
There are wonders to see everywhere, if you but slow down and look for them. Yeah, the Grand Canyon/Acadia Forest/Everglades or whatever your destination is a sight to behold, but that isn’t everything.
We all seem to do this at our own speed, although I think folks who try to drag their RV 2,000 miles in 4 days wind up being too tired to enjoy the vacation. Just my opinion.