I play on a 1060 6 GB and can maintain 60 fps most of the time (chugs down into the low 50s/high 40s in dense open areas, low 40s sometimes when in our well-lit base with a bunch of other people).

The graphics engine is currently throttled to use only 512 MB, so only having 3 GB of vram won't be a problem for you. The main issue will be with texture and object management regularly swapping things in and out, slowing down and heating up the graphics card (having my GPU fan throttling up to full speed within seconds of entering game is the only problem I've ever really experienced in regards to graphics).

If you're willing to take the risk with modding [beware that this game is still Early Access - technically a beta - and that any and all future updates may break mods which may in turn break the game until/if said mod(s) are likewise updated] then there are some mods that will allow you to tweak graphics functions as well as adjust/increase the amount of vram utilized and they have been known to do a good job of increasing frame rate. Ask around and somebody will point one out for you.