It seems MS will be focusing on better framerates then 8K at the very least. Xbox Team says framerate will matter most on Project Scarlett and as a PC Gamer Elite, I always prefer better framerates to better graphics myself but anyhow, here's a quote what the team has to say:
“Do I feel like I can get into the game as fast as possible and while it’s playing, how does it feel? Does this game look and feel like no other game that I’ve seen? That’s [the Xbox team’s] target,” Spencer added.
Just keep this in mind, both Resolution and framerates are limited by consoles developers. Xbox One X can do both 4K & 60fps "if" developers take the time to optimize their games and even so should take it with a grind of salt. Any issues you have should be taken up with the respective Developers.
So what's it gonna be to you? PS5=8K or Xbox Scarlett=better framerates 60fps? Make your choice.