Well they will pretty much perform the same, but I would go with the Ryzen 7 as it has a better upgrade path right now. The i7 isn't dead, far from it, but at least if the Ryzen 9 comes up, you can upgrade to that. Overclocking is trial and error and you should do some research on it. You are probably looking at 60 FPS at 1440p. Running another 1070 in SLI is easy, but you will need a high-speed SLI bridge (what brings the GPUs together). A good 1440p 144hz monitor should be decent, but that depends on your budget. This build is pretty much future proof for the time being. Of course you can get the 1800x, but I think that's a bit overkill for what you want.