Honestly there is nothing in that build that I would upgrade at this point. I think you are aware that this build is easily sufficient for pretty much any game out there right now.
As you go for more expensive high-end components, you face diminishing returns. At some point, you start paying a lot for small increases in performance. That is why I personally never feel like going way over midrange-ish components and why I think that replacing or adding anything in your current build is not worth it.
Maybe it would be more interesting to invest in peripherals instead. No doubt you have a great keyboard (this is, afterall, Geekhack) but investing in great headphones, mic etc. can make the experience so much better. Beyond that there is the chair, desk etc. Personally I spend a lot on those kinds of things, and I feel it adds much more than an expensive almost meaningless increase in performance.
