Firstly off the bat, Lowest possible or disable everything. Also if you run it with an MX170 or older GPU you should also look at 800x600, it really isn't so bad However the trick is with lighting. You can see brightness and facility lights. You can lower Brightness to get some extra performance BUT there is a sweet spot, not too bright, a little on the dim side, but helps significantly when you hit it to the point where my MX170 is able to go to 49% usage at the best of times and around 80 at the worst. Also self explanatory but no V-sync and Enable frame rate limiter, set it to 30-50 fps. Also when nuke goes off turn off facility lights, it massively hoards it gpu with the red lights.

And part 2: Gameplay: because yes, it impacts it (kinda)
Attachments: From what I can tell Night vision scopes and Telescopic scopes take a ton of GPU when in use so try to avoid those. Flashlights and lasers don't seem to do much and the other scopes also seem fine. Oddly enough when Larry dies he leaves particle effects that will take a good chunk of GPU usage so try and stay away from Larry if he is about to die, and don't break too much glass for the same reason: TLDR: No NVS and no telescopic, stay away from dead Larry