7700K will provide the cpu power to run any game well.
Yes, I7-8700K is better, but not likely to be significantly better.
Of more relevance is trying to use sli.
You would, no doubt win synthetic fps benchmarks, but your gaming experience is likely to be better with a single good card.
dual gpu is prone to screen tearing, and stuttering.
Some games do not support dual gpu at all.
In 2018, Nvidia is rumored to be delivering a single card stronger than anything available now. I would point towards that first.