- Upgrade Your CPU (i5 8500k will be 6 cores or i7 7700k / Ryzen 1700x) , Board , and Rams to prevent any Bottle Necks and the highest FPS.
-Get a 1080ti for 1440p / 144hz / Gsync Monitor - Still 2160p 60hz is midway , yes the 1080ti can tip 60fps @2160p in not in the majority of recent AAA titles. 1440p will be a sweet spot. My Recommendation: MSI Gaming X 1080ti.
For the Monitor go with this (Currently being sold @Macrotronics) - 1440p , Gsync , 165hz , 24inch
https://macrotronics.net/product_info.php/aoc-agon-ag241qg-24-inch-gaming-monitor-wqhd-sync-165hz-p-12113
Note:
As You Mentioned: " hardcore gamer that likes to max out everything while playing a game" to have the experience you attain for , your budget must be more relaxed and not restrained. Otherwise , the law of diminishing returns will apply.