[MENTION=426452]Squeezebox[/MENTION], I've used 170, 172.5, and 175 mm crank arms. I spec'd 172.5 mm for my builds and currently only have 170 mm and 175 mm crank arms.

Comparing 170 mm to 175 mm crank arms on two very similar bikes, I can spin up my cadence higher with the 170s and although there is a leverage advantage using a longer crank arm, it isn't something that I can feel. FWIW, both of my touring bikes have 170 mm crank arms.

Brad