you don't know what you can do until you try
as far as it goes for walking, 35 miles a day is moderate... best leg powered transit i ever managed was one day in venezia on a bicycle, 110km... damn you muricans... what is that... 85 miles?
venezia is very flat
i also found it was possible to do this kind of thing in the netherlands but every bit of slope you add to the equation you square root your distance
i live in madeira now and the slopes are typically 10-15% grade, sometimes they are so steep you almost can't avoid slipping on a few steps