I think most of us have a "natural" cadence. Mine is apparently around 82. But when I do a lot of interval training it goes up quite a bit. I like to do interval training on a flat course with two minutes at 85 and then two minutes at over 100. I try to keep this up for one hour. After a few days of this, it appears that my "natural" cadence increases to closer to 90-95 and anything less seems to be slow. In fact, 85 becomes a "resting" cadence.