I lead a ride for my local bike club once a month on my FG conversion. (When daylight savings time is in effect I lead my 15 mile Tue night training ride on the same FG bike.)It's a 32 mile ride over moderately hilly terrain. I use a 70" gear.
The other riders are on multi-geared bikes but an occaisional fellow FG rider shows up.

The downhill really tire me out but I can get up to 35mph by really spinning that gear but am cooked 1/2 way up the next climb.

If you are riding with a slower friend who is on a road bike, then riding a FG on rolling terrain will allow you to get a good workout too.