Processors do not improve that much between generations... even now with competition seemingly accelerating improvements somewhat. You will not see a very noticeable difference between a 7700k and an 8700k, and any difference a person could see would not be worth the $500 it would take to upgrade.
As an illustration, I currently have an i5-3470, so 4 or 5 generations ago, and I can still run every modern game with high/ultra settings in 1080p 120fps with my GTX 1070. I am only now updating my CPU/mobo to an 8770k. I will then probably keep that for 3 or 4 years minimum. (But I'll probably go through a few new graphics cards in that time period. 😉)
Anyway, save your money. Get a new graphics card in a year or two. You will see a...