Some resolutions will work, some will not. For a start, I'd try running (in the main FO2 folder after installing RPU/Sfall) f2_res_config.exeJust started to play the RPU and got one question. Are there a way to set up screen resolution 960x600? I've got a 16:10 monitor and play with 800x600 but it is a bit blurry. Manual setting of 960x600 through f2_res_config results in error.
If nothing else it gives you an idea of which res modes are supported, and should tell you what ratio they are. I myself am running on a 16:9 4k native monitor and I picked:
Mode=4 ; DX9 Fullscreen
SCALE_2X=1 ; Makes interface elements big enough for my old crappy eyes
GraphicsWidth=2048
GraphicsHeight=1152
Various other little tweaks and settings, but that was the basic setup that seemed to work well for me. Gave a look that didn't scale TOO much (the really high res modes show too much with the elements way too small. Just looks wrong to me, so I rolled it back to a point where yes, it's scaled and somewhat stretched, but IMO still looks pretty good).
For whatever it's worth. ^_^