There has been much discussion about the criteria of authenticity [See Bird, Eddie, Rafael, Crossley]. I am reminded of Geza Vermes who writes:
It is worth observing that the fundamental principle of New Testament criticism, namely that the burden of proof rests on the claim of authenticity, is to a large extent misleading. The thesis that in the absence of definite proof of its genuiness a saying must be declared inauthentic is logically false. Inability to demonstrate that a maxim assigned by the evangelists to Jesus actually stems from him, does not signify that he had nothing to do with it. It simply means that we are not in a position to prove that he had. Insufficiency of evidence does not automatically falsify a statement but puts a question mark after it. Likewise, lack of certainty is compatible with various degrees of probability.
I think the question ultimately boils down to what are we prepared to use, and what we do actually use in our various reconstructions and models of the historical Jesus. One may think the confession of Jesus' Messiahship in Mark 8 authentic, but how does that affect one's reconstruction of Jesus' claims to messiaship. I suppose I'm slightly more interested in what one does with the authentic material, than just declaring a saying authentic. For example, R. H. Stein's book on Jesus the Messiah would probably declare everything in the canonical gospels as authentic, but the picture he develops from their is sterile, or even myopic in it's reconstruction. Now I know one can argue that it wasn't meant to be a contribution to our quest but rather an aid for students, but I still question its usefulness and reconstruction. Or one could look at The Challenge of Jesus, based on JVG by Wright. While Wright certainly doesn't incorporate every single datum he considers authentic, the historical picture drawn is not only plausible, but I would argue probable. Thus what I find more important than merely assessing which saying or event is inauthentic or authentic is what we actually do with that data that we consider authentic. I recall reading Dennis Ingolfsland's articles on Crossan, Sources, Method and using much of the material Crossan considered authentic, but still coming to a radically different portrait. [He has quite a few articles available online that many are unaware of. Please, take the time to read his stuff carefully.] Therefore, let us consider what material we think is authentic and then let us start our historical reconstructions! Let us consider as much material as possible, even from Thomas and then slowly eliminate passages that seem to not fit the overall scheme of things. But then let us not consider this material inauthentic, but rather try and see if does have a place within our constructions, even challenging some of our models. Just a thought...  Geza Vermes, The Authentic Gospel of Jesus, pg. 419