The neurotypical limit is usually four, but can be raised with practice. Children with Down's Syndrome may not be able to subitize at all. Autistic savants can subitize up to thirty or more, with unconfirmed cases up to several hundred.
Part of the job involved accurately counting hundreds or thousand of screws. I quickly found that visually grouping screws into groups of 4 on a large table was the fastest way to be 100% accurate. If I tried to do 5, sometimes I’d get a sort of confusion/uncertainty, not being quite clear if it was really 5, or 4 or 6, forcing me to check. I’d go on to group these little piles of 4, into larger groups of 4. So I got really good at counting in 4 and it’s multiples, 16, 64, 256.
I can definitely see 4 being generally optimal, unless one can expect perfect visual ordering, which is possible with text, but rare in the real world.
No monkeys are discussing of subitization as a concept and how their species compares with others.
Just because a kangaroo can jump higher than humans doesn’t mean it can go to the moon before humans.
And, g factor.
https://en.m.wikipedia.org/wiki/G_factor
Even savants can have low IQ.
An adult Chimpanzee can rip your arms off. Pretty much all it's muscles are fast twitch. Of course you're going to have far better dexterity than the chimp, because you have a much better balance of muscle fibers.
That's the thing about intelligence, it's about generalization, not specific ability. A CPU can count to a billion in a second, nothing about that speed means it's 'smarter' than you.
This is also why we're going to have to come up with new metrics on abilities as we develop more general intelligence software to see how and where said software differs from humans.