Best technically is Intel 8600k, 8700k or 9th gen, but best value would be a 2600 for only 150$. You have a few options. A rx580 or gtx 1060 6gb should run 60fps max out for next couple years, but it's possible some games would require say high settings vs ultra.
I have an rx 480 which performs within 10% of a 1060 6gb and 60fps+ is no issue, but once in a while I find a game where i need to run on high vs ultra to get 60fps without any real dips. You may want to futureproof a bit and be 100% certain, but it cost more, kind of depends on what you want. For 1080p the 1070ti is a little overkill, but it would 100% get the job done in every game. The other 2 gpu will require some tweaking from time to time, but cost less.
Here are a few options.
You can get a 2600 / 580 for well under 400$
https://pcpartpicker.com/list/BLDRkd
Vs i5 and 1060 6gb for 500$
https://pcpartpicker.com/list/HprvBP
The 2600 and 1070ti (good model, well reviewed) is only 50$ more than a 8600 and 1060.
https://pcpartpicker.com/list/M7BLsZ
8600k and 1070ti +100$ at 650$
Technically the 8600k is better for strictly gaming, but if you stream the ryzen really wins. It's really hard to make a case against the 2600 at only 150$, it's retail is 200$, such a great deal. At 1080p you are talking about roughly 15% difference when using a 1070ti at 1080p and this drops to almost nothing once you play above 1080p resolution.
It's extremely tough to notice a 15% difference once you pass 60fps. That's like 72fps vs 86, seriously nobody is going to notice this. If you had a 144hz display in this example your going to want to play at 72 anyways. 90fps vs 108. 15% might sound like a lot until you see it this way and realize you won't notice these differences.