I've concluded that I'll just ride the way I want. My whole life, (and I've been riding my whole life), I've always ridden with lower cadences. I'm quite comfortable riding at a cadence of 65, and can do it all day long. I've tried spinning faster. Just doesn't work for me. Just yesterday, (Strava link), I rode a pretty flat metric century. My cadence average for the ride was only 70, and I thought I was pushing it a lot on that ride.

When I get to 85 or so, I start looking for a higher gear. On some of the steeper grades around my area, I've noticed that I'm only "spinning" at 45 or 50. I won't get to the top first, but I'll get there eventually. Until I figured out how to turn it off, my old Garmin would often complain while climbing that my cadence was too low.

p.s. Knees are fine. Has never been an issue.