You have to pedal HARD in the top gear of a road bike to reach 40 mph, even down a good hill.
Ummm... I dunno about that. Depends on the hill.
Out here in Western Massachusetts, there are plenty of long, LONG steep hills that I regularly reach 50mph - which is far to fast to spin with my low geared touring machine.
Of course, I'm a big oaf... so that helps!
Just tuck in, and hold on!