'Everyone' notices - even though most believers don't think about it much - that Jesus' speeches in John sound a lot like John in John's Epistles. (See my earlier post for general thoughts about speeches in ancient historiography.) That may not bother believers (and certainly shouldn't, in my opinion), but what does it do to our chances of doing historical reconstruction from John's Gospel?
First of all, John regularly inserts biographical and chronological details into dialogue. Philip tells us Jesus is from Nazareth. The Capernaum Jews later confirm Joseph is his father. Jerusalemites cite "Forty-six years" for the Temple's construction. John's disciples tell us Jesus is becoming more popular. Jesus tells us "it is four months until the harvest". The narrator takes on more exposition as the Gospel progresses, especially at transitional points and during the passion week, but the pattern does not fade completely. During the trial, Jesus, Pilate and the Sanhedrin all continue to provide exclusive narrative and contextual details the reader does not learn at other points.
The writer's method of including factual exposition within dialogue is consistent, so the issue of whether Jesus' speeches are verbatim is irrelevant. Any Johannine Historiography that analyzes the historical details in the fourth Gospel does so by extracting some of those elements from passages of dialogue. And that is my entire point.
If there is any basis at all for doing historical work from the Gospel of John, then there is no good justification for dividing between "historical" and "theological" content. Jesus tells us with equal plainness that, "I have preached regularly in the synagogues and the Temple" and that "the Father is in me". Although historical-critical scholars are welcome to throw out supernatural and metaphysical (spiritual) details on the basis of anti-faith, a faith-based historiography must accept that John is giving us both statements of Jesus as plain facts.
Therefore, the verbatim quality of Jesus' speeches does not necessarily matter. IF we accept John's testimony, IF we believe his deeper spiritual claims are the product of spiritual experience and/or divine revelation, and IF we consider historical details from dialogue as freely as from the narration, THEN, to be consistent, we should also treat particular details of a metaphysical nature as historical, even if they come from long speeches.
In doing actual reconstruction, of course, we had best judge the apparent meaning of each statement in a strictly practical sense. As much as possible, statements should be taken as spiritual facts, instead of being reinterpreted metaphorically or merely as 'spiritual truth'. Additionally, if a detail is unclear without philosophical interpretation, or if it is unclear how a predictive statement was or was not fulfilled, then we will do best not to rely as heavily upon such a detail in reconstructing events. Again, we are focused on events from a historical perspective, not on forming theological interpretations of meaning.
In short, if the Gospel writer tells us anything that plainly rings of supernatural spiritual activity, we will stand on faith to claim that spiritual event as historical.