just ticked all the various resolutions in the DSR option of the nvidia control panel, then the resolutions were available in game!
dsr can be a huge fps hit if you don't have the power to run it, because at the end of the day, you're rendering up to 4x the image and then having to downsample it.
i have to say, i barely noticed the quality change between 4K with no AA and 1080p with full AA.