That ride sounds like a right slog, the weather we’ve had!
+1 for the yogis. After riding round here for years, I still learnt loooooads of great trails from them. Unless you know you that you are pretty fast, I would start with a thursday or saturday ride as the tuesday one is often 3 hours and a lot more than 20 miles in that time!
http://yogicycling.com/
Also, even if you don’t have a gps or smartphone, join Strava just to have a look at what/where other folk are riding: there are loads of local xc riders that strava most of their rides and you will find plenty of circular-ish routes from coypool between 10 and 40 miles.
Failing that, wait for the lovely xc-steve to pop up on this thread so he can point you to some of the many massive online routes he has recorded.