I don't play fortnite. But with either CPU and the 980ti, at your 1080p res you should be pushing 100fps perhaps more, Don't forget though, with your 1080p monitor (most likely 60hz) although your GPU can push out more frames, you don't get to experience that on the 60hz monitor. Your monitor can only display 60fps. The rest is lost. You may run something like Rivatuner with an on screen display telling you your getting 100FPS+ but thats only at the end of the GPU pipeline, and is not whats displayed on screen (at least on a 1080p 60hz monitor). If you don't stream whilst gaming, and the cost is low, then the 6700k system will still serve you well for a time. If you want some longevity and a system capable of driving a high end card into the future for another 2-3 years, then I'd opt for the 1600x. All you would need is a GPU upgrade down the line (and maybe a nice monitor too!
) and you will still have an awesome system for gaming.