If you want to try DFs settings they're in the table below.
I've also put mine in too, which I'm very happy with and are a nice bump up in quality over X1X.
This is one of the nicest looking games I've played (I've not played any RTX titles yet). The lighting is simply stunning at times.
It's a shame the photos I'm taking with HDR aren't tone mapping very well down to SDR and blowing out the high light details. R* could do with sorting out local saving of photos too as they only seem to be 1080p on the Social Club (unless there's a way to get them at a higher res).
There's a good dog!
Edit: updated table with extra info about % effect on frame rate from Low to Ultra from Game Debate
Sorry should have updated my last post, it was not vulkan giving me the problems, it was having fxaa turned on, turned that off and the problem went away.
Good videos from HUB, cheers @Schumi 01
I've added their recommendations to my table too. Will give some of those a go. Of the ones to tweak from their base settings I'd go for Lighting Quality as that seems to give the most visual improvement as you step up over the other settings.