Being a Southerner in New York City, I always suspected this. There is no relationship between intelligence and speed. What is important is to deeply understand things and to think about their relations to each other. In math education emphases on speed simply create math anxiety and phobia, rather than great mathematical thinkers. From Fields Medalist Laurent Schwartz:
“I was always deeply uncertain about my own intellectual capacity. I thought I was unintelligent. And it’s true that I was, and I still am, rather slow. I need time to seize things because I always need to understand them fully. Even when I was the first to answer the teacher’s questions, I knew it was because they happened to be questions to which I already knew the answer. But if a new question arose, usually students who weren’t as good as I was answered before me and towards the end of the 11th grade I secretly thought of myself as stupid and I worried about this for a long time. I never talked about this to anyone but I always felt convinced that my imposture would someday be revealed. The whole world and myself would see that what looked like intelligence was really just an illusion Now that never happened. Apparently no one ever noticed it, and I’m still just as slow. At the end of the eleventh grade I took the measure of the situation and came to the conclusion that rapidity doesn’t have a precise relationship to intelligence. What is important is to deeply understand things and their relations to each other. This is where intelligence lies. The fact of being quick or slow isn’t really relevant. Naturally, it’s helpful to be quick, like it is to have a good memory. But it’s neither necessary nor sufficient for intellectual success.”
Laurent Schwartz, Fields Medal earner, as quoted by Dr. Jo Boaler in EDUC115N How to Learn Math (MOOC)