You have a relatively well balanced gamer now.
It is not clear if a cpu or gpu upgrade will be best.
If you upgrade your cpu, consider buying a I5-4690K or a I7-4790K and plan on a conservative overclock.
If you go the i5-7600K and an overclock, you are going to want a Z270 based motherboard as well as some DDR4 ram.
If you want a graphics upgrade, go stronger than a RX580. Perhaps GTX1070.
It is only two tiers higher on tom's gpu hierarchy chart, they recommend three tiers or you may be disappointed if you do not see magical results.
http://www.tomshardware.com/reviews/gpu-hierarchy,4388.html
A SSD is a very good performance upgrade, but 120gb is too small for a C drive these days. Buy 240gb at least.
And... the only ssd I would buy today would be Samsung 850 evo. They are better and more reliable performers.
5 year warranty tells something.
My stock approach to the cpu vs. gpu upgrade question:
Some games are graphics limited like fast action shooters.
Others are cpu core speed limited like strategy, sims, and mmo.
Multiplayer with many participants tend to like many threads.
You need to find out which.
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To help clarify your CPU/GPU options, run these two tests:
a) Run YOUR games, but lower your resolution and eye candy.
If your FPS increases, it indicates that your cpu is strong enough to drive a better graphics configuration.
If your FPS stays the same, you are likely more cpu limited.
b) Limit your cpu, either by reducing the OC, or, in windows power management, limit the maximum cpu% to something like 70%.
Go to control panel/power options/change plan settings/change advanced power settings/processor power management/maximum processor state/
This will simulate what a lack of cpu power will do.
Conversely what a 30% improvement in core speed might do.
You should also experiment with removing one or more cores. You can do this in the windows msconfig boot advanced options option.
You will need to reboot for the change to take effect. Set the number of processors to less than you have.
This will tell you how sensitive your games are to the benefits of many threads.
If you see little difference, your game does not need all the threads you have.
It is possible that both tests are positive, indicating that you have a well balanced system,
and both cpu and gpu need to be upgraded to get better gaming FPS.
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