Just got back from 12 days in Brittany which was fairly lumpy - nothing huge, but seemed to be either up or down, very little flat. And always a head-wind, even riding a loop, it was always against us! Anyway, ave speed was alway 10mph, +/- 0.5mph, over an average of 50 miles a day, with camping/cooking gear on board. This is as per the computer. Usually started riding at 10am and finished about 5pm, with coffee/lunch/crepe/patisserie stops as needed. We gave up worrying about the speed - we could nearly always talk going up the hills, and it was just a guide as to where we could hope to get to each day.
50 miles a day seemed about right to us, did 60 once on an easier day, just how it worked out. You could do 60-80 in a day if you specifically need to be somewhere in a certain time, but you probably wouldn't enjoy it too much - depends on what you want to get out of the trip.
Certainly increased my respect for the guy who cycled around the world at 100 miles a day!