It really all depends on the individual. 350 miles a day would be a really easy and relaxed day for me. That would be in the realm of a Saturday ride for me. 500 miles a day is a longer day, but plenty doable. I did have a more than wanted day turning 800 miles plus small change in one day. None of that was on an Interstate slab. If you are going all back roads/highways miles take longer, if taking the Interstate slab, the miles get eaten away pretty fast (I don't care for the slab, but have ridden on them at times of necessity)

BA has Freak, 160mains, 44pilots, air mix3 1/2 to 4 turns, BUBS dresser dogs. Never had more fun on any bike - 2nd bike 2008 RIIIT