You have a reasonably well balanced system now.
It is not clear what your most effective upgrade would be.
FX-8350 is not very effective from a single thread performance point of view.
That is very important for many games.
It is not clear how many threads you can effectively use.
Most games will use 2-3 threads. Multiplayer with many participants can use more.
Here is my stock approach to better understand what you need:
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 threads 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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If you need single thread performance, the answer is kaby lake.
If you need many threads ryzen is good.
I would discount threadripper on two fronts.
1. It is new with likely teething problems.
2. No game is going to use all of those threads.
Aug 21 should bring the coffee lake processors. I think I would wait to see what that brings.
Likely, the big deal will be 6 core processors.
Here is a recent test using a GTX1080ti comparing i7-7800X vs. 7700K titled 6 vs. 4 cores for gaming.
https://www.techspot.com/review/1445-core-i7-7800x-vs-7700k/
Takeaway is not much difference, but the cheaper 7700K wins by a bit because of faster single thread performance.
For anything less that a GTX1080ti, I would think that ryzen or kaby lake $200 processor would do the job.
Either would be a big upgrade for you.
But, if you are entertaining a top graphics card, look for a top cpu to drive it.
What would be your graphics card upgrade?
It makes little sense to do a small upgrade, like to a GTX1070. You are likely to be disappointed if you do not see big results.
More likely, you are looking at the GTX1080ti which you mentioned.
Today, it is as good as it gets for a single card.
Vega looks like a GTX1080 competitor at best.