The easiest way to see how well that would work would be to set the resolution to something like 1440p and cropping a 1080p image out of the middle of it. 1440p has 78% more pixels, and is roughly 78% more demanding.
Maybe in the future UE4 or a game engine would support foveated rendering and allow rendering a larger screen at lower resolutions around the edges to allow SSR to reflect stuff that is off screen. But that isn’t possible right now.