I7-6700K for $200 is a steal, and by far the best for gaming.
Few games can use more than 2-3 threads, so 8 core processors are not much useful for gaming.
Past that, games depend on the performance of the single master thread.
The single thread passmark rating of the E5 2670 is 1618.
For the I7-6700K at stock is 2236; more with overclocking.
FX-8350 is even worse with 1504 rating.
As to graphics, you may win fps benchmarks with dual gpu, but your gameplay will be better with a single good card. I would think a single GTX1070 would be about right.