Looking at the actual I7 8700k price, I would recommend that you either wait until the price calmed down or go with Ryzen 5 or 7 second generation or wait for the I7 97xx.
For 4k gaming, which can still very limited by the GPU even with 2080ti, an I5 8xxx should enough. I7 8xxx or anything with more threads is however better for the future proofing.