I've raced on 172.5, 170, 167.5, and 165mm. Only on 165mm can I "run on the pedals" where I hold high RPMs out of the saddle. With the other crank lengths, I would have to sit at certain RPMs in order to get more RPMs. Basically, the crank length limited how fast I could spin out of the saddle.
This might get better at even smaller crank lengths.
The downside of going shorter is that, for a given amount of torque (whatever your legs can offer each pedal stroke), the gearing must come down. My from-the-hip calculation is, to keep the torque feeling the same, go up 2 gear-inches when you go up 2.5mm in crank length or go down 2 gear-inches when you go down 2.5mm in crank length.
I posted the actual formula that I found in
Bicycling Science (D. G. Wilson). But, I don't have it at hand.
The takeaway is: Pick the crank length that complements your pedaling style.