Is there a way in a shipping build of a game that I can have the resolution be 1280x720 and have it full screen on a 1080p monitor?
I think you need to look at this How to improve game thread CPU performance in Unreal Engine - Unreal Engine and find out why it’s going so slow, rather than compromising on the window size to help it.
Reduce the resolution scale…
Or simply use r.setres 1280x720f