Diversity of a population plays a role too. If I'm well below Feynman level (and I am), then there's a possibility that I can slightly improve my cognitive abilities without any negative consequences.
My experience with nootropics (racetams) seems to support this, as far as it is possible for anecdotal evidence.
Just thought you guys should know about this. Some work that argues that humans should not enhance their intelligence with technology, and that super intelligence probably never evolves.