The better question may be 'what is the intended use for a particular crank length?'
I have bikes in 170, 172.5, and one in 175. Given my style riding I prefer a 172.5. Like iab, I can't tell the difference in normal riding. In sprints or climbs, I can. I spin more than mash. All my bikes have nearly identical contact points. A large change in crank arm length will most likely have an effect on KOPS, if you size by that method. In any case, the fore/aft of the saddle may have to change from 'normal', depending on the ST angle...
No set answer to that question, too many variables.
Are you trying to fit your new Primato? If so, it has a laid back seat tube, you may have to go shorter cranks, forward saddle position, and a shorter stem. Not ideal, but may work, fit-wise. Take a bike that is comfortable, and try to match contact points. I'm assuming you are not a kid, and maybe not as limber as you once were. Comfort on a bike is foremost. Duplicate what you know works, and make small changes from there, after your body tells you to.
Most of my bikes have the same saddle/bar setup, so it's easy to make some simple measurements. With different bars and saddles, it would get more complicated. I strive for center of BB to top of saddle, tip of saddle to center of stem, and handlebar drop/hood position as close as I can get.
Contact points, to reiterate.