$400 Upgrade - CPU, GPU, or Monitor?

If you had this system, what would you spend $400 on right now? (To better gaming capability for upcoming AAA titles.) Games I want to play include Battlefield 1 multiplayer, and upcoming titles such as Destiny 2, Assassin's Creed Origins, and Anthem.

23" 1920x1080 60Hz Monitor
Pentium G4560 (w/ Cryorig H7)
MSI Z270M MORTAR
Sapphire Nitro+ RX 570 8GB (doubles as mining card when not gaming)
G.Skill 8GB DDR4 2800 (single-channel)
Kingston HyperX Savage 240GB SSD
Hitachi Ultrastar 2TB HDD
EVGA 850W B2
*NZXT S340


This is the system I have to play with after selling off my 4790K + GTX 1060 to dive into ether mining. I can always put the RX 570 in to a separate mining rig I already have running. I also have another 8GB DDR4 stick that is different than the G.Skill, won't run in dual-channel. I've thought about going with Ryzen 5 and then having an extra system for someone else who is currently using a Core 2 Duo to do homework and web browsing.

So these are the options I'm considering:

1.) i7-7700K + matched 8GB RAM

2.) Ryzen 5 1600X + MSI X370 Gaming Pro + matched 8GB RAM

3.) EVGA GTX 1070 SC (or similar) (Doubles as a mining card when not gaming)

4.) 27-28" 4K Freesync Monitor and wait for RX Vega
 


Yeah that's what I figured. I just really have an all of a sudden urge to try out 4K. Maybe that's the thing.. maybe I should try it before I decide to buy it. You and I both KNOW the 7700K will do it's job, but will 4K satisfy my gaming needs? Probably not unless I have a GTX 1080 Ti and a better CPU, I don't really know.
 
You have an urge to scratch an itch. That's not motivation for a 1070. Not enough meat on those bones when the 1080Ti is what will quicken mining and prepare your PC for 4K and gaming. Although in your position I would first invest in some higher end cooling such as the Noctua NH D15 or the Kraken 62. I would address the cooling at the same time I purchase the 7700K. Then the RAM and finally the 1080Ti.
 


Before I got in to mining I was going to get the Kraken X62, I bought the NZXT S340 case just to fit it. But is it really necessary? I can always disable turbo boost (if needed) until I decide to get a better cooler.
 


I can only say what I would do. The 7700K does have a reputation of running too warm. I would be proactive. If you instead had 4GB the need for RAM would eclipse that of the cooling. The immediate need would be more RAM because many games NEED more than that.
 


Thanks for that, some games the 7700K leaves the G4560 far behind, but other games they are neck and neck.

*You know what, the 7700K will guarantee a smooth gaming experience no matter what. I think I've settled it.
 


Yeah, I remember that last year it wasn't really an option to go 4K unless you had some serious hardware. I guess it's another generation or two before mid-range 4K is doable. But then again Destiny 2 will run at 30fps on the Xbox One X (Scorpio), I figure i can't do much worse than that by tweaking settings.

Aside from the $400 I'm looking to spend, I just sold my slowest RX 470 4GB for $349 on eBay. Maybe I'll use that to get a 4K monitor and then see what RX Vega is all about.