According to the on-line crank arm calculators, I should be using around a 155. I currently have 170 on both my upright and bent. The 170 seems okay on the upright, but too long on the bent, where I have a difficult time keeping a smooth motion going - either the downstroke feels too far away or the upstroke is too close, depending upon where I have the seat.

(I make this observation every time we discuss this subject .... which I think has been about 4 times in 2007)

I do find this to be an interesting subject, that bike shops never mention when I talk about being fit properly on a bike. I've been trying to find a bike with 165s on it for several months now and haven't been successful.