Folks, I've just spent a bit of time looking at crank lengths. I won't pass judgement, but I will say from my experience a longer crank works better for me, especially on the road, unless clearance is a factor. I currently use 172.5mm cranks on my crit and road bikes and 165.o on my track bike. Most 'crank length calculators' tell me that I should use 165mm cranks all of the time, but it doesn't seem to matter that much in practice. Unless of course you are using long cranks on a steep velodrome or in a tight-cornered crit - then you risk bottoming-out a pedal. Or if you swap bikes a lot (I once crashed spectacularly at a road circuit in Warriewood, Sydney, when I was balked by a car mid corner. I forgot I was on my Colnago with 175mm cranks and hit a pedal at bottom dead centre. I was too used to using my 'crit bike' with 170mm cranks at Heffron Park and simply forgot to stop pedalling around the only sharp corner that mattered). It can get dicey.
Anyway, some resources for you:
Sheldon on cranks
Netally goes into detail on research
I enjoyed the read and I think I've decided I'll stay with what I've got, thanks. 172.5 isn't causing me any pain, so I'll stick with it for now. However I may drop from 53 to 50 teeth on my big ring... hmmm.