Knott has posted demonstrations before showing that your ideal cadence has to do with your individual proportion of fast-twitch to slow-twitch muscles. So just like each engine has a different powerband, each person has a different powerband, too.

Still, 60 rpm seems excessively slow to me. Too slow and you're risking your knees. I'm a pretty slow-twitch endurance type, and the natural cadence I fall into for both easy riding and easy running is right around 85 rpm.

No matter what your ideal is, it's useful to train at high cadence. That helps smooth your pedal stroke like not too much else. Among other things, the lower your cadence, the easier it is to fall into pedaling in squares instead of circles, which not only is inefficient, it's extra hard on your knees.