Would be wiser to just let the new consoles come out, let next-gen console games and their pc ports come out to see what kind of pc it takes to run those maxed out at double the console res and double the console framerate, as you need at least that overhead to account for increasingly underperforming pc ports over a console's lifetime if you want it to last instead of having to upgrade every 2-3 years.
I agree in general, but I would add that the Series X seems to be targeting 4k native (though for how long who knows), and that a lot of times ports take more PC power to run later on because they're more enhanced. Red Dead 2 for example, to match the Xbox One X settings you not only drop to 30fps, but also run most graphical options at medium or low, and some are even lower than PC low. I put Read Dead on Xbox One X settings posted by Digital Foundry and it ran at like 100fps.