No, I am not kidding. If you watch the track sprinters, cadences of 180-200 are commonplace. The BMX champions can spin at >180 out of the saddle. On a rest day during the 2012 TdF, team Sky had a small-ring sprint competition for fun, and to keep their legs loose. Cavendish tweeted that he had won with a cadence of 227.

Downhill on my FG I start to get lumpy, and therefore nervous, at around 150. But I don't do enough work on leg speed, I'm lazy about it.