You'll never get the same performance for the same cost on PC. They showed forza horizon 3 running at 60 FPS/4k on the scorpio, in a stress test with wheather effect + the maximum amount of cars on screen, while only using 66% of the available GPU power. And that was on a version of forza that was not even yet optimized for the scorpio, all they did was spend 2 day updating the engine to run on scorpio. I'm not sure how much the scorpio will cost, but the NVidia 1070 struggle at running forza horizon 3 at 4k at over 50 fps. Getting anything more than a 1070 will likely cost you close to the price of the scorpio just for the GPU.

Specs to specs, PC would seem like a good deal for the price, but with all the optimization that goes into tweaking consoles to make them perform better on games, its rarely the case for a PC to outperform a console for the same price. For example, they announced a hardware implementation of DX12 into scorpio, which isn't available on PC yet. We don't know how much this will affect performance, but its the kind of things that plays in favor of consoles.