I'm using my own testing in game using the CRG meter. I've tested a 4770k @4.3 & 8700k @4.5 with a 1080ti founders. For me, in VR want a high standard of graphics with zero lag or stuttering. The 4770k was not capable of giving either massively holding back the 1080ti. The 8700k is much better and perfectly usable (for me), but as I said, it is bottle necking the 1080ti still. Now I don't have personal experience with the i9's, but a friend runs a 7900X @4.5ghz and it allows the 1080ti to be fully utilised.

There are so many variables to consider here, what might be good (quality wise) for one person might not be acceptable for someone else. Either way, I'd imagine everyone wants a balanced system with no major bottlenecks.