1. Can you close your side applications, background junk and all to go game? like can your OS be clean and let it focus resources on the game instead of w/e else? If you can do that this processor satisfies the 1070 Ti for high refresh rate in all accounts and will be much the same of at least lets say a stock i5 8600K.
2. You are doing this for higher refresh rate and the i7 8700K is the to go chip for that as it's identical to the i7 9700K on this regard. You will be by all means eliminating any bottleneck chance to the 1070 Ti... or a 1080 Ti... RTX 2080 Ti? You see it's really the best and you might be misjudging how much your 1070 Ti requires. Do this if you have the money as think it as a luxury.
This CPU however can be justified if you want to leave a bunch of junk open alongside your game like 200 tabs in chrome yay, content creation blah blah bah
3. This is the CPU you pick if you'll actually do *serious* work, since it prioritizes that at much better price while it can game all the same albeit bit lower fps... you know it's the people who aren't in this for a luxury alone for them, and the whole idea of price to performance rises up.
Awesome pick, AMD brought performance cost so much lower it should always be praised my brother was saving for an i7 6900K he managed to build an entire 1800X build for cheaper than the CPU price for an on pair performance lel.
The way I see it you should just get the i7 7700K, it's basically the i7 8700K with 2 cores less and lil bit less cache, so "IPC OC" and w/e is really much the same and its single thread performance which Still is the most important thing on gaming is on pair with the top.