This is indeed known in the psychological practice in general (it's called "processing speed"), but most lay people aren't aware of it. Ask your friends if they ever got a professional IQ score and if they got the the different scores you describe. You tend to see it with people whose parents notice a high intelligence with learning difficulty and fight for thorough diagnostic testing and educational services.

Common tests don't explicitly measure it, but the test design either implicitly demands processing speed (timed tests, or rapidly spoken prompts/questions) or avoid it.