The most impact will be the GPU. Regardless if you got a 2nd hand 8700k or new intel or AMD.
Do not skimp on your GPU. Also relating to that - your monitor.
As ive droned on before, for me bigger is better. 16:9 the most practical for all uses. Unfortunately theres no decent 32" 144hz 16:9 2560x1440p monitors available. The LG one thats out has very poor viewing angles compared to other VA monitors (VA still my choice).
60hz is fine for me. If you're also cool with that a good quality non-curved 60hz 32" 16:9 1440p monitor can be had for reasonable $.
e.g. $367 for this samsung.
https://www.amazon.com/Samsung-SD850-WQHD-2560x1440-LED-LitMonitor/dp/B00L3KNOF4/ref=cm_cr_arp_d_product_top?ie=UTF8
Alternatively, if you prefer 21:9 theres a ton to choose from but youll pay more and its less viewing area, have to stuff around with a quite a few game HUDs, not as good for all the 16:9 content (youll only have a 27" viewing area then), etc, etc.
So what GPU? 2nd hand 1080ti or 2080 or new super variants of the 2070 or 2080