Starfield's performance is locked on Xbox, Todd Howard says, causing worry about the space sim on PC, but a God of War Ragnarok dev comes to Bethesda’s defense.
No Man's Sky runs at a very stable 60fps, I personally know people who have wrangled it up to 120fps. I know they don't have the same underlying tech, but they're very similar in terms of gameplay (from what we've seen)
They're a wildly different level of detail though. The NMS physics engine is pretty simplistic, mostly effecting NPCs and a very few physics objects. Starfield is like other Bethesda games, tons of little items and junk that all have their own physics and interactions.