If you’re using a 1080p, then all should be fine. But if you prefer your 4K screen for whatever reason, you can do what I said. It should net you exactly the same performance numbers because it’s still rendering at 1080p, only upscaling to 4K.
Either way, whatever works best for you. Just don’t run at native 1080p on a 4K monitor. That will make things jaggy and ugly, particularly text.