A friend has a GTX 1060 in her system, with the graphics card market being somewhat rational I was thinking an upgrade might make a nice gift. i7-6700k, 32GB ram, GTX 1060.

A bit of research says that at 1080 or even 1440p almost anything faster would get bottlenecked by the CPU(apparently a 1070 might make sense), but what about 4k? I know that's less dependent on CPU power, but that only holds so far.

Obviously a comprehensive upgrade is the better option, but that's far out of a rational budget for a gift.

If I found a good deal on a 7th Gen i5 or i7, would that make much difference in GPUs it would be rational to upgrade to?

Actually, I have an i5 7600k that I'm not using, and my also unused i3 6100 would do the job for my vague plans for that system. So if that would expand sensible GPU upgrades, assume I'll throw in the i5.