I could do about 30 miles on a sportsbike until I couldn't put up with the pain anymore ;D
On my "Sports Tourer" I can do about 100 miles before I need a break, and 250 mile days are comfortable.
On my Tourer (sit up and beg GS Adventure) I can do 80 miles non-stop on the stock seat before numb bum sets in and I need a break. 300 mile days still OK though.
If I put the Sargent or Kahedo seats on the GSA then I can do 160 miles non-stop and 350 plus many more mile days.
There are many different reasons for back, leg, bum, neck and arm pain on long distances. Its all down to the individual and as Jon says, the ergonomics of the bike. What works for one might not work for another and everyones pain threshold/fitness level is different. This is why there are so many different aftermarket "solutions" for you to spend your money on.
