I went to 165 arms on my TT bike several years ago. For most folks the trade-off of being able to get somewhat lower with the same hip angle generates more speed, especially true on longer TTs.

With that my best TTs and track Pursuits were on 172 cranks. But those were also my absolute peak all time fitness and power periods as well. The reduced flexibility because of age and injury made turning over the longer cranks more problematic. But if I over laid my mass start track stuff over my road stuff which would be a 165 to 172 5 comparison, I never saw any significant differences.

What I did notice was the slightly shorter cranks were easier on my knees overall. I run 170's on the road for what it's worth.