From my experience, trying to mess with the game settings only makes image quality worse with no real performance improvements. So leave it at high and use plugins to fix performance
Givemefps plugin. Set hair multiplier and curve to 16.
Scene stripper: delete all lights. Add only 2 invisible lights manually. There are tons of giant guides on lighting, but the basics are simple: you need a key light (a main light in front of your subject, angled in a way that looks good to you; I like to use a spot light and angle it from below) and a fill light (a weaker light on the opposite side to soften harsh shadows so they don’t go completely black)
Browser assist: If you have too many .vars, you can use the var manager feature, to disable all but the ones you need for that specific scene. May improve performance AND load times if you have hundreds of .vars.