Thanks, I was under the impression the CPU was the bottleneck. Seeing as upgrading the RX590 would cost quite a lot like you said, Ill go for the ram option.GPU upgrade would have the biggest impact. Then RAM increase. Distant third would be CPU upgrade. Obviously, it also depends on the game. But I'm talking in general terms.
Given current GPU prices, though, I think buying more RAM would be the most cost effective way to boost your performance. The RX590 is still a serviceable card and you'd have to pay well over the odds to upgrade on it.