• Can I define custom resolutions bigger than 4096 pixels wide ?
    Yes, you can define custom resolutions bigger than 4096 pixels on OS X 10.9.5 and above, but only if you use SwitchResX 4.5 or newer.
    OS X prior than 10.9.5 cannot manage such resolutions.

    (Note that scaled resolutions can be defined up to 32768 pixels in all macOS versions).

    In all cases, defining such resolutions doesn't mean that they will all activate, depending on the driver and macOS limitations.