As others alluded, the resolution matters. At 4K, you're GPU limited. Your difference between a 2700K and the fastest CPUs will be a couple percent.
At 1080p however, you constantly have to redo the draw calls and recalculate all the rules, physics, player positions, etc...This takes time for every frame. As the frames are being drawn quicker because the resolution is lower, the more often the CPU has to redo the scene. So a fast CPU matters for low resolution. But then you also need a really fast monitor to go with it. At least a 144Hz.