Depends on the effects you're using, for example if you only activate some sharpening and some color correction you'll barely see any difference in performance but if you use one of the more complex shaders like ambient occlusion frames can drop by 5-10.
Destiny 2 (Running at 5120x2160 with Ultra Settings minus Film Grain and Chromatic Aberration):
Note: Despite only having a GTX 1060 and a 1080p 144Hz monitor at the moment, I use DSR to ramp up the resolution and graphical settings before taking a screenshot at the expense of the in-game framerate being poor. I also tend to toggle off in-game UI. Afterwards, I just switch the resolution back to native.