The Prince of Nothing. The Prince of Nothing. The Prince of Nothing. I'll say it as many times as I have to to get people on this blog to read it. The Prince of Nothing Trilogy. The Darkness That Comes Before. R. Scott Bakker.

True, Anasurimbor Kellhus is one of the "mutants", even to the point of the author explicitly stating the Dunyain spent a few centuries running a eugenics program to get an intellect of that stature. But the later books of the trilogy also go into some detail about the rationalist training Kellhus undergoes with the Dunyain, the methods he uses, and even a little of the social structure of the Ishual monastery. He's one of the perspective characters, and we see him using his techniques; there's always a strong sense of "I could do that", which remains right up until I actually try. And there's no better work to demonstrate the "sense that more is possible", or the ways in which a real rationalist would be the polar opposite of the "Spock" prototype, or a bunch of other things (disclaimer: many don't become fully clear until The Thousandfold Thought, the last book in the trilogy).

The Dunyain conception of rationality isn't exactly like our own, and rereading it recently there were a few things that bothered me, but overall it's basically the story of a fantasy hero who is as good at probability theory as Aragorn is at swordfighting, with similar results.