Depends on why I'm traveling. For camping trips, I try to limit the time spent driving to 4 hours or less for a 4-day camping trip. Gives me a good range of campgrounds within that distance, and I am not exhausted from the drive.
For sightseeing trips, I have gone as long as 8 hours (not in the RV) between stops. That was a very long day, so I try to keep it closer to 6 hours max. I also have a trick for determining how long to stay in one place. I do a bit of research and identify those sites/activities that interest me. Then I count up those activities based on the expected time needed. So, if an activity will take less than 4 hours, I count it as 1/2; if it takes more than 4 hours, I count it as 1. Add those up and that's how many days I stay in that location. Works great as I have plenty of time to see what I know I'll enjoy, leeway time to relax, add in a couple things, etc.
