A very cool interview.
I tweeted to Perkins and asked him about the gear ratios they use in Keirin racing. His reply: "ratio is between 3.85 up to 4.20! Pace of races change every time, 500m is between 26-30sec!"
Also, a friend told me that Keirin is pronounced "KEE-ding". I think that's right. EDIT: I am corrected below...