When I first came back to fixed, about 6 years ago, I found I had an odd spot in the mid 20's where my cadence was choppy and I wasn't happy, above and below that I was as smooth as I was when I was riding fixed in the late 1980's, I never quite figured out why but found the answer was to think and make an effort to drive the pedals round, these days I rarely think about what the legs are doing. My problem with high cadence comes with very cold temperatures, zero and below, when my right calf can cramp up and go into spasm, not nice over 150rpm.