Depends a bit on personal taste and how close you have moved the screen, but personally I would prefer a widescreen res for immersive screen/cinema. Ultrawide may be overkill, but 16:10/16:9 are typically well suited for immersive screen/cinema.
The main reason for the 4:3 FullVR recommendation is that with FullVR widescreen resolutions most of the time are a waste of GPU power since a lot of what gets rendered is never visible.