I saw many people not believing the performance mode was on 1080p and then I got the game 2 days ago and I have to admit I agree with them, I was like "mmmh no it must be at least 1440p I almost don't see any difference on the image quality with the 4K mode" and it really is 1080p, wow, then one of the best 1080p I've ever seen, the checkerboard must be responsable of this.
Btw to me the performance mode is the mode to go, the difference between 30 and 60 is, at least to my eyes, obvious, the 30fps mode is sluggish as hell. but the difference between 4K and 1080 in this game is quite irrelevant. And also the performance mode is the default mode when you launch the game, so it's the decision that made the developers and I understand why.