Would I notice a significant difference if I went to performance?
Can stick it on auto and it will try and hold 60 FPS though you will notice it dropping quality in places with softer distant graphics and/or more obvious trails behind certain objects. Personally I'd rather play like that though than turn RT off.
I would turn off chromatic aberration, film grain and depth of field - doesn't really gain much performance wise but they add nothing to this game and just seem to have been slapped in to tick off features rather than used in a way to enhance the visuals.