Honestly, if you only play Fifa, then I would consider getting a xbox one x. As a pc gamer, I feel it blasphemous to say it, but you will have a better experience on the xbox. I dont know if the xbox one x will play Fifa at 60fps, but I would be surprised if it did not run it well. It is not a demanding game. I prefer high refresh rate over resolution, but it also depends on the game. Quick twitch shooters need a high refresh rate, but for a sports game like fifa, the refresh rate may not make as big of a difference.
Yes, you 6600k will be fine with the 1080. Truth is, when you move up into higher resolution, the bottleneck moves form the CPU to the GPU. So at 4k, the CPU is not working nearly as hard as at 1080p.