So I was riding with a (for me) fast group, and I had to spin higher gears for my standards, 44/16 to be precise, much more efficent. The whole ride was entirely flat, about 75 miles long. Did a thorough strech after, I have no problems now.

I was kind of brainwashed from all the pro high cadence talk I read on the web, so I guess I was tripping I have to ride like Lance or something. Spinning somewhere between 90 and 100 on flats is quite adequate I think now, going over 100, especially without clipless pedals is not so efficient it seems. So I guess some more miles in my new favorite gear will develop my legs enough that I won't be killing my knees when suddenly lowering cadence on climbs (because it won't be dropping so much now).