The facts are .... There is a 3% power diff for 5 mm length. Usually it is only noticed with an IGH like a SA hub with big gaps. I went from 165 to 180 and it changed everything to the better. Comparing these at the same speed, the shorter one will do 100 rpm while the 180 will do 91. BUT the relative circumference speed will be EXACTLY the same. Newton's second law. Knee extension is worse for higher, but offset some by less downforce.

I find the shorter one is gutless. I am 5'8". Tour bikes are mostly using 175s now, not bad.