My situation's probably unique, but I went from 175mm to 170mm cranks, and it made a world of difference in comfort. I've got joint problems developing from many years of distance running on hard pavement, and the smaller diameter rotation just made the aches and pains go away. Due to my mom's medical issues I'm somewhat paranoid about joint replacement so I'm doing everything to avoid it/put it off as long as possilbe. I haven't tried 165mm cranks, but if I find one cheap in a square-taper format I might swap it onto one of my bikes.