Does anyone have anything to offer here?
I've been using 175mm cranks for a long time now. I even have a pair of 177.5mm on my TT bike. The science behind the longer crank length is leverage: the longer the lever, the more torque you can apply. However, a longer crank also means a longer dead spot in the pedal cycle, as well as a higher knee on the top part of the cycle which can reduce your ability to get a low position in the drops.
I'm trying to work on a lower position these days as I find my current position too upright, but with my current setup I feel I have less power when in the drops as my breathing is somewhat restricted. I'm on a fairly small frame for my size, so part of it should be addressed by lengthening my saddle-to-bars distance so that I'm more stretched out, but I'm also thinking of trying a 172.5 crank length to see if it helps alleviate the problem - I'll be higher up by 2.5mm, and my knee at the top of the cycle will relatively be 5mm lower. But will I lose power?
Experimenting in crank length means you have to consider forking out for the cost of a decent crankset that might not work for you anyway, so it's not that straightforward a thing to experiment with.
One decent article I've come across has a lot of interesting points but in the end I'm no closer to being able to decide.