What length cranks do you use on the road? The informed opinion around here is that you use anywhere from the same length to at most 5mm shorter on the track than on the road. So if you are using 170mm cranks on the road, then you might go down to 167.5mm on the track. It's very difficult for your legs to constantly switch between a bigger difference in road and track. The cadence that you develop on the track will be determined by the gearing that you choose, higher the gearing then lower the cadence and vice versa. Everyone has an optimal power band, and that will ultimately determine your preferred gearing and cadence, not the crank arm length. I know very tall sprinters who use long cranks up to 175mm, and have a very high cadence, and pursuiters that pound huge gears like 96 - 100 with shorter cranks. Myself, I use 165mm cranks for both road and track, but then I'm only 5'-3", so that's about the only choice I have.