I found by doing this my po went up even though i did not adjust the fps.
I think u need to make the game control your graphics file and not have the file so the game does not affect it if u know what i mean.
All i know is it did not help me it made mine worst but if it works for some people then good.
I still think the best way of getting a lower po and higher fps is to change the detail in the mirrors ie shorten the distance and detail that the show.