Made a trip last summer from Anniston, Al to Minot ND 1600+ miles pulling a trailer. Did about 700 miles first day, 450 2nd day and 600 3rd. Talk about tough don't like doing that, but I had to. I like to keep if around 350 to 400 miles a day.
I saw terrain mentioned in one post in determining your travel endurance but not wind. A very windy day can really wear you down in a hurry as we've learned crossing the plains states. Otherwise we can do a 500 mile day if necessary but generally stick to the 300 to 350 rule as well, know your limits and travel safely. Good luck!
No one has mentioned traffic either. I camp in Los Angeles at Dockweiler Bch. RV park frequently to check in on my elderly Mom. Just trying to get out of the traffic can take three hours. With four or five lanes of traffic going in one direction and the mental focus it requires, wears me out. Three hours of being stuck in traffic feels like the equivalent of eight hours of rural driving to me. (And I spent most of my life living there fighting it daily.)