I have never been sensitive to crank length riding 170 and 175 mm etc. and would have to look to even know what one I was on. I do understand some people are more sensitive.

I like to tell people the 5 mm is the thickness of 3 penny’s stacked up or something like a 3% change in length.

If you know that difference will be a factor in your riding then by all means go for the 165 arms.