You are good.
Any ram that exceeds standard speed needs to have extra voltage and is technically overclocked.
However when that setting is done by the XMP settings, I don't see how that would void a warranty.
Why not ask Corsair, who should be able to give you an authoritative answer.
The second partners are the cpu and motherboard.
Your motherboard supports ram speeds even higher.
And, if a i7-8700K is not suitable, then nothing is.
Technically overclocking to extreme cpu voltages can and will void your warranty,
The expectation is that a K processor will have the multiplier raised to reasonable limits and will not exceed the maximum spec voltage.
I think that is 1.5v.I think Intel has a way to detect over voltage on chips returned...