You will always have a bottleneck one way or the other either CPU or GPU, it really depends on the game, the settings, and the resolution you are playing at. At 4k resolution you will be limited by the GPU in most games, if you are playing at 1080p - the CPU will be your limiting factor but you should still have 80+ fps.
Your CPU is still top tier for gaming, best option is to overclock ( a CPU upgrade would only net maybe 5-10% performance and only in some situations).