my i7 7700k runs from 4.2 ghz to 4.7 ghz and i wanted to know if it bottle necks my rtx 2080 and if i should upgrade to a i7 8700k
Key word there, "some games". A bottleneck will depend on the application it is running. On one application, the CPU may be the bottleneck, on another application, it may be the GPU. This is why we look at "most games" instead of one game.As long as it is just gaming (with no streaming workloads), the 7700K is still quite adequate/good/relevant, and in fact,, still out frames almost all Ryzens in the vast majority of games....
(The TechPowerup link comparison above used a 1080Ti, a still fine GPU, but, naturally there might be a bigger disparity in CPU scaling with the very best GPU, i.e.., a 2080Ti...)
Here is another cross section of gaming results comapring different CPUs, but, using a 2080Ti...(shows still very good results with stock on OC'd 7700K), but shows up to 35-36% improvement in some games' (FarCry at 1080P) average frame rates comparing stock 7700K to stock 9900K, and the difference shrinks to 29% when both CPUs are overclocked