I'm doing Tour de Wyoming this week. Constant pedaling. Most grades are 1-4%. I've done more pedaling in this tour than any other due to the terrain.
Even with the thousands of miles I ride I still have to concentrate on my pedaling stroke.
What I've observed over 400 miles this week is that if I concentrate on spinni g all the way around I can increase my speed 1/2-1 mph. If I go from riding on the hoods to the drops I can increase my speed another 1/2 mph.
This is on flattish terrain and keeping the heart rate pretty constant.
The longer I ride the more concentration is key.