Assuming all conditions are the same except for time, if you go on a ride at an average speed of 13 mph that you previously did at an average speed of 12 mph, how much extra effort did you put in to go that one average mile per hour faster? About 27%... e.g., instead of 65 RPMs, same gears but a little over 80 RPMs.

That brings up an interesting issue. Supposedly, the ideal crank length for maximum production of power, irrespective of the size and conditioning of the rider, is 145. So, if going from 165 to 145 enabled you to easily cruise at about 80 RPM instead of 65, all other things equal, you'd more easily put out the added effort necessary to generate about 27% more horsepower.

Interestingly, that is something I could check out fairly easily– I have a pair of Ride 2 crank shorteners. Closest I can come to 145 with my setup is 141 (and raise my saddle 24 mm). But then I'd be in a more aerodynamic position so... we're not talking science here and do I really need to get there about 4 minutes sooner?