I'd rather do 30 - 40 mile days when I am cycling touring, especially if I'm hauling my own stuff. It leaves you time to enjoy where you are, talk to people, take pictures, explore interesting places. Also, you don't have to ride so hard that you can't enjoy the local cuisine.

If you're currently riding at a ten mile an hour pace, that's 4 hours of riding time just cover the 40 miles. That leaves you a reasonable amount of the day to be a tourist.

V.