Found a way to drastically improve the frame rate without fiddling around with the INI files.

Simply don't play in Fullscreen mode, instead set it to Windowed + Borderless.

It'll still be fullscreen, but not exclusively. It will sync with the desktop instead.

FPS performance is now 10x better.

By default, the games sets everything to Ultra/High on my PC (GTX970) but the FPS is almost unplayable in Fullscreen. Cant even play on Medium with FSAA and Shadows on Low, there is just way too much mouse movement delay.

Now I can play in Ultra with silky smooth performance.

Fallout INI files and nVidia control panel settings are all default!