Agree in the hip angle limiter being a reason for potentially going shorter. This trend was driven by the Tri world. The idea being you can run more effectively after a TT on shorter cranks. An issue we don't have to deal with.
I've given 165's a try and didn't really feel any advantage. They feel about the same till I get tired. Then I feel like I can battle fatigue, stay on top of a gear better on 172's. No real numbers to back that up.