I've reduced the duration of my rides dramatically, just getting bored...so what happens over 80m I can't recall. But the last year or so I've been alternating cadence; running at 90+ for a while, then dropping to 75-80, picking gears appropriately. It seems I'm still feeling fresh after a few hours. Sometime I mash up hills, sometimes I spin. Overall speed seems to stay about the same.

In spin class, it's always 90+.But on my bikes I've gone to longer cranks, and that seems to have knocked 5rpm off my average cadence.