Best I do in N Florida's slightly rolling and sandy-soil woods is 10.5 mph ( 1:41 for 18.3 miles) based on riding time and about 9.9 mph based on total elapsed time. I used to run about 8 mph, but started pushing higher gears, upgraded my wheels and went to Stan's noTubes conversion to run lower pressures. Each change made a very measureable difference.

I'm lucky to average 7 mph in the N Georga mountains where I also bike a lot.

Al