This will give you a LARGE boost in performance (Or rather, it should.). Especially in high NPC areas. I'm sorry if this is in the wrong section, I just wanted to help out as it took me a bit to discover these but it was very helpful.
In the ~ (command) menu, type "toggleemotions". NPC's will not display facial emotions any longer, and will give you a bit of a framerate boost.
Ontop of this, if you're looking for a large boost all across the board and the cost of graphics, open up your Fallout.ini AND Falloutprefs.ini and find this line:
Go ahead and change that to 0 in BOTH ini's. It will not work unless you do both.
What does this do? Simple, specular mapping is what causes those reflections you see on everything (Stand near a light source and move your camera around. Your armor may reflect, and metallic objects / streets will reflect.). This will make your game WAY uglier but should give a large FPS boost.
Hope this helped! Sorry to wall of text you.
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