As you might already know there's a correlation between big-5 O, IQ (even if small), and N MBTI preference.
This means that people that tend to score as N, tend to score as having high O on the big-5, and tend to score higher on IQ tests.
Now, we have to analyze the path of causality which is present here. In my opinion, it goes like this:
Higher IQ then
High O and High N
So this means that irregardless of their real functional preference, high IQ people tend to score higher on N than lower IQ people - because let us face it there are certain questions in MBTI tests that can be equally tied to smarts and intuitive preference.
In actuality, my observations are a tad more complex than that. There is a dependancy on the first function of the individual.
Let me give you an example:
ESFP Se dominant will score as ENFP because he/she will recognize him/herself as irrational but also as intuitive.
ISFJ Fi dominant will score as ISTJ beecause he/she will recognize him/herself as rational but also thinking.
We can go on and costruct a simple algorithm from there, so that ESxPs will score as ENxPs, IxFJs will score as IxTJs, ISxPs will score as INxPs, etc.
This of course in case of very high IQ.