My so called average cadence displayed on my garmin computer always ends up in the 70's, even though I hardly ever ride with a cadence in the 70's, because coasting and stopping (periods of little to no pedaling) lower the value displayed by the computer. I find my sweet spot of speed and endurance on flat-ish terrain to be in the 90's, my highest speeds are achieved while mashing in the 80's, and climbing completely destroys my cycling so I can't comment on that until I do more of it and figure it out.

Hey UMD - how did you get that graph?