I exceeded 50 miles per day average (by 3 mpd!), but the 10 mph on-bike speed was spot on.
Now I just plan on those figures, maybe add 10 miles a day if somebody else is carrying my gear.. If there's not hills to slow me down, it's flat and the wind comes up. I only remember two significant tailwinds, the longest 10 miles -- the rest of the time the wind was in my face, or it's a crosswind with a hefty headwind component.
Take what the road gives you. Enjoy it. Push a bit, but not so much that you'll hurt tomorrow's ride.