My last and only course in psychological testing was probably late 1970 or early 1971. That said, I'd personally be very uncomfortable predicting ultimate limits for a person above a certain level of brain development. (Say, the "basket-case" level.)
One problem with trying to quantify creativity issues, there are a lot of "eye-of-the-beholder" issues. A kid makes a finger-painting. I see smears; you see a masterpiece. Is the kid creative? Depends who gets asked.
Since Science is unable to measure and weigh such does it exist?
Depends on your definition. The human brain, anyone's, is a finite thing. But can you imagine all the things that could come out of that brain in any situation? No. The brain responds to the environment, and if you're leaving the potential environmental stimuli unbounded, you can't put a bound on what might come out of the brain. Anyway, that's my best guess.
I am unable to even imagine the extent of a Mind. Yet to tell the truth, I am impressed with a notion that there is more 'reality' in the Mind than in what we see with our eyes. Does Science recognize such a preposterous idea? Not in this life.