I recently installed a power meter and just used it to get up some rather steep 15%+ climbs.
At my weight and lowest gearing (34f 30r) at a sustainable power level for my fitness (225w) this translated to a seated 35-40rpm cadence.
Higher cadence would result in heart rates of 190bpm+ which I couldn't sustain over the climb without stopping.
This is MUCH lower than what I usually spin at (95-100) and while I made it up the hills, I am concerned that this could cause damage to my knees/body if I continue to do this without losing weight or increasing power. (Working on this :) )
I have searched, but there doesn't seem to be much on this topic.
A triple is not an option as I am doing this for fitness/fun and in the long run the compact I just upgraded to (50/34 from 46/36) will be enough once I get more KM into my legs.
These climbs were 1-2km in length with up to 130m elevation gain (Cat 4), but the question is more about doing this for extended amounts IE (Cat 1 / HC)
Standing for that long of a climb is not achievable for me at the current fitness level.
I didn't feel any discomfort in my knees, but everything I have read suggests high cadence cycling but I am not there fitness wise yet on these climbs.