Depends on the game and the resolution/frequency of the monitor. An i7-7700k is strong enough to handle any game at any resolution/frequency and not be a limiting factor. The gtx1070, however, is not capable of full detail settings at 60Hz on a 4k monitor in every game, even many 1440p/144Hz games. For those settings you'd need to move upto a gtx1080 or for 4k a gtx1080ti.
So gasaraki is entirely correct, in certain circumstances, the gpu can and will be a limiting factor when faced with monitor extremes. For a standard 1080p/60Hz monitor, it'll be the monitor itself that will be the bottleneck, the i7/1070 both being more than capable of maximum settings and having room to spare.