OK,I looked at another thread the OP made:
https://forums.overclockers.co.uk/threads/is-my-ram-bottle-necking-my-pc.18801838/#post-31384442
They are using dual channel RAM.
They also have a 34" FreeSync monitor which is 1080p,so I assume its one of the 2560X1080 ones??
Can you clarify what model you are using OP??
They also play PUBG.
I would say looking at that,perhaps they should try the CPU upgrade path first. It also looks like they say their system RAM is maxed out too.
So OP,if I were you try the platform upgrade for now and stick with the GTX780TI and see how you fare with the game. Since you have FreeSync it might be worth looking at an AMD card at a later date,providing its not overpriced,but the latter part is very important.
From what I gather from looking at some reviews of PUBG its not too bad with VRAM usage,although I don't know if the later updates have changed that.