Called itBut... Pro is only competing with S and X is way out of its league!
Ubisoft: AC Origins To Run at 4K/30 FPS On Both Pro and Xbox X - NeoGAF
tl;dr AC Origins runs on both consoles at 4K/30 using dynamic resolution scaling. XBX may have less resolution drops but the end result will be imperceptible to the human eye. Supplemental resource: Digital Foundry's tech breakdown of AC Origins where they confirm the game is using checker board rendering on Xbox X.https://www.youtube.com/watch?v=e8oPvbpVGP0