Historical Jesus studies have been exploring this for decades. You might be interested in the results of the Jesus Seminar that happened in the early 90s. A bunch of scholars got together and voted on which pericopes they thought were authentic or not. There have been many criteria for authenticity proposed -- and there have been a lot of critiques of those criteria. Nowadays, scholars don't really take the conclusions of the Jesus Seminar seriously. But this just goes to show you that people are taking into consideration these questions. If I were to give a book recommendation, it'd be <em>Jesus: Lord, Liar, Lunatic... or Just Freaking Awesome?</em> -- which obviously plays with Lewis' schema you discussed above and chapter one of which can be read here