Yes they do (Scott H. Young is way smarter than me and he has developed a method of soaking up really complicated ideas in a matter of weeks or days).

I don't think this is a useful question though, there is no reason to think that the gains in ability to utilize LW-style rationality are linear. I think its more likely that there is some threshold level of intelligence that is needed to make use of the techniques then the gains get smaller. Other skills are similar - calculus, basketball (where the property is height rather than intelligence), physics etc.