[yurishimo]

That's how most raytracing is done these days anyway. The game is rendered at a much lower resolution, the raytracing math is applied, and then it is upsampled to the target resolution.

If you set the target resolution to 1080p, not much changes in the render pipeline except the that final upscaling step. To get better quality, the lower resolution is bumped up so there is more data to work with for the upsampling, but the scaling performance can be very hit or miss depending on the game as the engine itself often can play a huge role in rendering performance.

As far as rendering the 1080p image at 4k, yea it works fine, but there will always be little artefacts that remain for those looking for them. 1440p seems to be the sweet spot for gamers today, but 4k is really nice for when you're not gaming as most online video is now made for dual use on televisions.