Some of the 3700X 4K numbers are around 45-70fps with a single 2080ti. If you want a CPU that can carry you through 2 or 3 successive GPU upgrades then you want something that can feed the equivalent to 2080ti SLI. No idea if it can but being behind now doesn't auger well for the future.
4k is great for large tv's etc - so if you are gaming on these fair enough - but given we are already in a very small segment as it is......Im not convinced a lot will be pc gaming on such hidef desktop monitors
but fair enough, if you are then 3900 / 3950 when it appears is probably the best option (if not Tr when it appears)