There are two types of iq: static and dynamic. The static one is mainly influenced by genetics, and it makes up like 90% of your iq score. The dynamic one can be exercised, by reading, maths, problem solving, etc. There is no evidence that the stuttering “deformity” in the brain (if it even is that) also affects the static iq. I think we as stutterers fall along the same normal distribution of static iq as non-stutterers. But I do however think that stutterers in general are less involved in sports and other social things, thus spend more time on school and studies, maybe read a lot because they have few friends. Or play a lot of games, where gamers also show to have on average higher iq than the average population. These are life choices, that result from stuttering, which makes a smart / intelligent person. And this would increase the dynamic iq. I don’t remember where I read up on these two types of iq however but I think it’s a pretty established view.