Cpu sets the fps cap regardless of resolution. Put in a powerful graphics card, the stronger ipc of the 8700k will deliver more pre-rendered frames but probably at the cost of higher cpu usage. Depends on game and how cpu involved they are. Ai, physics, maps, sound, multiplayer + preparing 100+ frames is a big job for even the best cpus today.
8700k is a great cpu and can handle a lot. So can top end Ryzen's. Ryzen's may not set as high fps cap due to slower ipc but they too get the job done without hitting a usage wall while still giving decent fps.
Zen 2's ipc is rumoured to be a lot better too, competing with 9900k. If true, fps cap can only increase.