I have started playing Witcher 3 in immersive mode with sharpening set to 2.0. When I start the game Vorpx warns me with a red message for too low FPS but when I am in the game and look at the FPS using FpsVR I see almost a constant 90 FPS.
Use the built in FPS counter (ALT+F). vorpX has two render-pipelines running in parallel: the game itself and a second one which renders the final image to the headset, both can have different frame rates. The built in FPS counter displays both.
In cinema/immersive mode you can get away with rather low game FPS. Even 25-30fps may work fine in that case if the game isn’t a super fast shooter.
There are already too many options in the menu, so to reduce menu clutter a few less important things are hotkey only. You can map ALT+F to your controller if you consider it important enough to be available anytime while you play standing.