Your claim that 12 cores isn't useful today is why I'm writing no. Many apps like video editing use every core and some use GPUs to power the work along.
Even if your game did use more cores the extra cores let the usual PC use those cores for trivial background tasks that could cause a less core machine to randomly get too busy.
And all this is moot for most gamers as the REAL POWER is in your GPU choice.
FOR 1080p gaming, even at 144Hz which you don't have you can get by with any current gen i5 and the 1060 GPU. This has been kicked around so many times that I won't write at length here.
Also, check out the builds at https://www.reddit.com/r/PCMasterRace/wiki/builds
No i7s there. Why is explained.
Which would you get?
The price difference between a build with 8700K and a 8600K is R$414.31($127.48), 8700K and 8400 is R$812.24($249.92) and 8700K to 1600 is R$1104.99($339.99).
The Ryzen one seems to offer a lot for its price, but, considereing that a game lasts about 2/3 years to develop, we would see Ryzen's real results (utilizing all of the 12 threads) in about a year or two. The 8700K looks like the most solid one, but also very expensive. And the i5s look like the most balanced ones for today's market, being the 8600K a solid 8700K competitor if we consider price-performance.
This build is just for gaming, no streaming or working. Since I don't have a 144hz 1440p monitor yet, let's say I wanna play on 1080p(where the processor is most stressed) with high frame rates, being ahead of the necessary hardware. And before I forget, any build will contain a GTX 1080, and same specs, CPU's the only different part.
*All these values look very expensive because I had convert Brazil's currency (R$) to US Dolars, so these values have included taxes, such as inflation and customs duties.

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