Infinity intelligence is a very vague and probably ill-defined concept; to go to an impossible extreme, if you're capable of modeling and predicting everything in the universe perfectly at zero cost, what would it even mean to be more intelligent?

That is a hard limit on intelligence, but neural networks can't even reach that. What is the actual limit? No one knows. Maybe it's something relatively close to that, modulo physical constraints. Maybe it's right above the maximum human intelligence (and evolution managed to converge to a near optimal architecture). No one knows.