The answer @fasterthanever is with something called gain ratio (the distance the pedal moves as a ratio of how far the bike moves). Probably best if you google it I might mess you up by explaining further. Edit: Thought the title was gear not gain. Thought I was being helpful but, you are way ahead with gain ratio: Gain ratio=radius ratio x chainring teeth/rear cassette teeth. Longer cranks=less radius ratio which=less % gear than a shorter crank.
Having been on 165’s from 172.5’s for many years (geared bike not fixed!!) nothing changes with power or cadence. You’ll find you just self select by feel and shift as required. What you might notice is how a shorter crank feels over the top. That is where these shine. If they can reduce even slight impingement then they will improve pedaling for sure.