We are retired, so we have more options.
Normally we plan on 250-300 miles/day and plan for stops, sightseeing, etc. along the way. Enjoy the trip as well as the destination.
However, 350 miles/day is about the max I look at. Maybe 400 if timing is right. We don't like to rush leaving in the AM, and want to avoid rush hour at the end of the day. If we are traveling in sparce population, 400 is possible. But then we try not to travel the next day. get up, have a leasurely breakfast, take off, arrive in time to relax, have a nice dinner, time after dinner to relax.
We have on occasion pushed 450, but not often. In most cases we plan on closer to 250/day, spend time sightseeing, etc. and enjoy rather than being tired.
Driving our car we regularly do 750 mile trips/day as a matter of course. But average speeds are MUCH higher, stress is lower.
Now if the trip was all freeway (something we avoid, usually travel secondary roads for the scenery, etc.) 450 miles wouldn't be that bad.
the other factor is that when not towing, DW and I pretty much share driving, and we can each nap.
When towing DW occasionally will drive on sparce freeways, but doesn't really like to. Nor do I. So I do virtually all the driving. She knows she could drive in an emergency, but doesn't really like it when towing. So on occasion on the freeway she will tow from one rest stop to another so I can catnap.
2011 Keystone Outback 295RE
2004 14' bikehauler with full living quarters
2015.5 Denali 4x4 CC/SB Duramax/Allison
2004.5 Silverado 4x4 CC/SB Duramax/Allison passed on to our Son!