I am the outlier here by far. A consequence (or benefit!) of having many years of long-distance driving experience, and limited vacation time.
Typically, I average 60mph, which is easily attainable by my short E450 Class C when not towing. That is generally a 68-70 mph cruise at 2500rpm and 8mpg. I'm also good for generally 14-16 hours of windshield time, so just about 1000 miles in a day can be done. Or, I'll sneak out of work early around 3pm to beat rush hour, and drive to 11pm or midnight, getting in the first 400 or 500 miles of a trip before doing a WallyWorld stop.
Right now, less miles a day is not an option. Maybe when I retire, but that's not for another 12-15 years.