The additional problem is that there is a period of adjustment to a new cadence which IME lasts at least a couple of weeks. That greatly complicated the task of, for instance, doing hill repeats at different cadences and watching the power meter or distance/time. I would try varying the cadence by a small amount, maybe 3 beats, and checking that, before deciding anything. Also, best cadence varies a lot with power output/HR. Higher outputs require higher cadences or you only last 5 minutes. Low outputs, like resting, and an 80 cadence might be the thing.