I share your dimensions and age, a few years ago I had to have surgery on my knee and noticed on my mtb with 175mm cranks there was a noticeable slight pain across the front of the knee, so I tossed on 170, the difference was obvious and the pain went away. With my road bike I had 172.5 and while they didn't cause me pain I found them less comfortable to pedal and also found the 53/39 to be more limiting with my more limited training due to family obligations. So when I built my cross bike I went with 170 and between the 48/34 crank and the shorter length I found it was easily the first bike I grabbed without thinking about it, just sold the road bike after not riding it for the last 2 years. I might experiment with 165 on the next bike but I won't go longer than 170 ,just seems easier to pedal.