You got a very good GPU that will get the job done. You got a crap CPU with no hyperthreading.
if you are playing Fortnite and streaming on the same box, you need way better CPU than that and you need to turn all your in game video settings down to their lowest values. Unfortunately, that makes the game look like crap as well. Given the systems I have and tested with, I'd recommend 6C/12T minimum fo 720p at 60 if you even want to get the quality level up for streaming Fortnite. Consider a Ryzen 5 1600X for your next purchase to go along with your GTX 1070 and I think you will be much happier. For those wanting higher resolution, you need at least a 8C/16T to get good quality. However, at high resolution Twitch limited to 6000 bitrate, it look like sh*t (my opinion). On YT, it will look damn good if you know what you are doing.