I know someone will eventually pop in with a video of a Keirin or track racer spinning up to 180 RPM, but I've done a few rides with a friend who likes to really spin up on downhills, last time we hit 40 on a descent he was in his 53-14 I think, and must have been spinning smoothly at 130 RPM. Impressive to follow him and see the form. I start bouncing at about 110, but he regularly trains for very high cadence and it works, keeps him fresh at the end of races.