There is simply no exact cutoff.
It depends on the games you play, the resolutions you play, and the Graphics Card you own.
In addition, Vulkan and DX12 can use the CPU more efficiently in two ways:
1) more able to use every core fully, and
2) more efficient usage in how draw calls are created (less CPU cycles to do the same task)
Now game developers can decide to utilize more of the CPU for tasks if they want. For example, the game/benchmark AotS can use a lot of your CPU because it's the type of game with many, many units that need CPU calculations for all their battle calculations.
AotS is not typical. (arguably it's intentionally overkill to demonstrate Ryzen's threading performance and GCN GPU optimizations)
*Even if your CPU gets lower performance than a better CPU it still may be sufficient to give you an excellent experience. Would going from 80FPS to 100FPS give you a better game experience or not?
So... it's complicated.
In addition, we can estimate CPU requirements (on average) based on the gaming consoles. I estimate the XBOX ONE X (new XBOX) performance per core as roughly a PASSMARK SCORE of:
1000
Total performance I'd estimate as: 6,000
Your CPU if overclocked to 4.5GHz is roughly:
per core: 2,600
total: 9,500
Now the console is underpowered on the CPU which is why many games have difficulty hitting 60FPS, though 30FPS games are usually mostly solid so the AVERAGE is likely above 40FPS for those games.
*My point with the above is that it looks like cross-platform games should tend to have no issues hitting a solid 60FPS on your system, so it should be a matter of adjusting the graphics settings to hit the FPS you want.
Specific games:
You can look up different, modern games and find CPU SCALING charts to give an idea. Again, many of these mostly eliminate the CPU bottleneck at 2560x1440 or higher anyway. For example:
https://www.techspot.com/review/1006-the-witcher-3-benchmarks/page5.html
SUMMARY:
So the answer again is complex. It will NOT change quickly aside from individual games so you can reevaluate later.
It's also worth noting that money may be better spent on a GSYNC (NVidia GPU) or Freesync (AMD GPU) monitor as even if the FPS is slightly lower your gaming experience is much smoother. In asynchronous mode the monitor draws a new frame when the GPU tells it to so we don't worry about hitting a specific FPS cap to avoid issues like stuttering or screen tearing.
So it's possible your system can last you FIVE YEARS more if you want.