You can run games at any resolution you want with vorpX. The higher, the better the image quality. Recommendations are: 1280×1024 (performance), 1600×1200 (balanced), 1920×1440 (quality). 4:3/5:4 resolutions are generally best for vorpX, not widescreen.
Please also make sure to update the Fallout 4 profile from the cloud. Yesterdays Fallout 4 update broke the Direct VR scanner, which you can address by downloading the latest version of the “Fallout 4 [vorpX]” profile from the cloud.
You may also consider to set Antialising to “Off” in the Fallout 4 launcher. Both AA modes used by Fallout 4 blur the image.
Just like you normally would when you play a game on your monitor. In Fallout 4 that is done in the Fallout 4 launcher. It often makes sense to run games windowed with vorpX, which will allow resolutions higher than your monitor supports in many games.