I had not realised how expensive the 6700K would be...that is too much and you can get a 8600K/9600K or 8700K for that price. You have a three options, number one, go get the 6700K or 7700K whatever is cheaper...
Number 2, spend the money on a better GPU, this will provide an immediate boost to frame rates and I have seen GTX 1060 6GB in Romania for 1.139,27 RON or roughly Euro 270
https://www.pcgarage.ro/placi-video/palit/geforce-gtx-1060-6gb-ddr5-192-bit-2/
Even better jump up to a GTX 1070ti for 1.849,99 RON or roughly Euro 390...This would give you the biggest bang for buck immediately and you frame rate jump would be huge..
https://www.pcgarage.ro/placi-video/inno3d/geforce-gtx-1070-ti-x2-v2-8gb-ddr5-256-bit/
Option 3 is moving to the Z370 or Z390 or Ryzen platform though that would cost a minimum of Euro 600...I personally think, upgrade the GPU now and when you next look to upgrade, move to the new platform...
Right now a GTX 1060 6GB or Radeon 580/590 or even better a GTX 1070ti would provide the biggest increase in performance for you.....Moving to a 6700K or 7700K will mean you are stuck on an older generation platform and that Euro $430 you have to spend would be wasted....
Hopefully others can jump in with better suggestions as this is a tough one....