Well that obviously depends on what you are putting on your screen:
- complex 3D graphics: it will slow down a lot since each pixel that has to be rendered for the scene adds work
- 2D graphics: if you have complex graphics (eg illustrator and perhaps PS) it may actually be faster since you're scrolling less
- normal apps: by my measure, there is no slowdown whatsoever. I run 19W GT 710s x 2 + Intel HD 530 IG and there is no slowdown on my 3 x 4K monitors (plus a 1080p monitor), which is a total of about 26 million pixels. I'm running an i5-6500.
