I was wondering this same question. I used to ride 170 many years ago and then switched to the 172.5 for the leverage purpose. Sounds like I am the same size as you and I think I noticed a difference. When I rode the 170s I felt like I was really turning the cranks in a smooth even spin and was very fast at sprinting. With the 172.5 cranks I do not feel as smooth it feels like I have a dead spot at the top of my revolutions, so I have been considering going back to a 170. If the 170 allow me to spin more smoothly all the way around I would think it would be more effecient whether climbing, sprinting or just riding the flats.