I note what you say about the Ryland’s papyrus but I find it somewhat disingenuous. It merely testifies to the existence of the 18th chapter of John’s Gospel being in existence possibly as early as 120 A.D. and it says absolutely nothing about the reliability of the text which we have of any of the Gospels apart from these five verses. You know and I know that the earliest complete copies of the Gospels are Codex Sinaiticus and Codex Vaticanus which are both dated to the middle of the fourth century A.D. There are considerable differences between these two codices and fifth century Codex Bezae as I am sure you are also well aware. From investigations being carried out by a colleague, David Inglis, on the Internet, it would appear that the text of Luke in Codex Bezae is much closer to the text known to Marcion than the one we have today. I would recommend that you purchase a copy of "The Text of the New Testament – its transmission, corruption and restoration" by Bruce Metzger and Bart Ehrman. Perhaps you would like to explain to me how it is that eleven manuscripts contain the story of the woman taken in adultery, not in John chapter 7 but in Luke chapter 21. This is merely a single example of the problems involved in in the transmission of the disciples’ impressions of Jesus, initially over anything up to 6 decades and after that over another two centuries during which later Christians made modifications to the text which they had received in order better to represent their beliefs and practices at the time and the better to polemicise the text so as to make it attack those whose views they disagreed with such as the Gnostics. I can produce example after example of both these practices and problems. This in fact is what I am engaged in on a daily basis with many different colleagues who seek to find a solution to the Synoptic problem and in the process are forced to engage with the actual text. Many of the difficult passages are in fact highlighted in the notes at the foot of the page in the New Revised Standard Version.
I am well aware of these issues. Actually, I am reading Metzger’s book on the canonization right now, by coincidence. All this is helpful and useful to arrive at as close as possible a version of the original. However, in no case that I know of is there a really important theological question raised by these differences. I like to see the forest and not just the trees. The forest is in pretty good shape, in my opinion. Whether or not the woman caught in adultery belongs in Luke or John is not very material. What is material is whether or not this event happened. I believe it did. I am not saying the location of the original in the text is absolutely irrelevant, but it is quite secondary to ask which gospel it was found in originally. What is important is that this story represents an actual event. I believe it does. I believe it was part of the oral tradition about Jesus before it was incorporated into the gospel. In fact, I am prepared to conclude that the story of the woman caught in adultery was actually not in the original Luke OR John, but that it was inserted by a later editor because it was such a well-known part of the oral tradition. I believe that oral tradition in a culture which is familiar with it, and in a context in which many of the hearers are eye-witnesses to the events is quite reliable.
So, I just cannot get all that worried about whether Bezae or Sinaiticus is the best MSS. I study all these things a LOT—perhaps almost as much as you do, but I have a different perspective than you. I am leaning more toward being a bit more skeptical of Sinaiticus than I used to be and slightly more confident of Bezae, but in the end, the theological difference between Bezae and Sinaiticus is not significant. Jesus is God in both. Jesus dies on the cross in both. Jesus works miracles in both. Jesus is love personified in both. Jesus fulfills the messianic prophecies in both. Jesus is born in Bethlehem in both. Jesus is the son of Mary in both. In my opinion, you are missing the forest in all your looking at the trees. The “Synoptic problem” is real, but it is a minor problem. None of the examples you have given me have changed my mind about that. I have read plenty of Ehrman. He is incredibly biased, but he is still a very good scholar. Nothing he has to say changes my picture of Jesus to any significant extent. Does it affect it at the edges? Yes. That is part of why I tolerate Ehrman’s blatant bias in order to learn from him, but I note that while he might be right in the “minors,” he is wrong in the “majors”. He believes that Jesus is not God. He believes that the Bible is not inspired by God. He is completely and utterly wrong in the biggest questions!!! He carries presuppositions that push him to wrong and even at times irrational conclusions.
About the Rylands Papyrus, you say "it says absolutely nothing about the reliability of the text which we have of any of the Gospels apart from these five verses." I believe this is an exaggeration. The existence of this manuscript confirms, for example, that the book of John was in existence at this time. This is significant. The actual words in Rylands are the same as those in our other extensive and relatively reliable manuscripts. This is corrolary evidence and support for the general reliability of other manuscripts. The existence of a manuscript of John within fifty years of its original writing is useful as a support to the reliability of the text. Does it PROVE that our oldest versions of John 12:45 are reliable (to choose an arbitrary verse)? No, but it is one small but significant piece in the case for the reliability of the New Testament. So, I do not agree with your statement that it says absolutely nothing.