What comment would you make about the very great differences between the MT, LXX & Samaritan Pentateuch?
Evidence implies that our Greek New Testament text is a nearly perfect descendant of the originals. The case with the Old Testament is significantly different. The time period between the last New Testament book being written (about AD 90) and the oldest manuscript which can be dated with confidence (The Rylands Papyrus, AD 125-130) is quite short, while the gap between the last OT book being written (about 430 BC) and the oldest manuscript we have (some of the Dead Sea Scrolls which are as old as 200 BC) is relatively large. The Masoretic Text was created by Jewish Masoretes about AD 800. It is separated from the originals by well over one thousand years of copying and even some editing. The Septuagint (What you are calling LXX) was translated from Hebrew to Greek about 200 BC, but our oldest manuscripts of the Septuagint come from AD 350. The Samaritan Pentateuch has an even more scant evidential history. For these reasons, our Old Testament is plagued by a fairly significant number of copying errors and even some non-accidental editing done by copyists. The result is that the amount of difference between the Septuagint, the Masoretic and the Samaritan Pentateuch is rather significantly greater than the differences between the oldest New Testament manuscripts.
I am not sure what kind of comment you are looking for. From my perspective, there are two "see the forest rather than the trees" questions to be asked.
1. Were the originals inspired?
2. How significant are any changes made from the original in terms of theological, doctrinal or important historical information?
My conclusion is a VERY strong yes on the first for reasons you are well aware from having looked at the kind of evidence I present at my web site and from conversations we have had. The fulfilled Messianic prophecy, the type/antitype connection between the Old and the New Testament, the remarkable historical reliability of the Old Testament, the scientific reliability of portions of Genesis, the theological consistency, the consistency of the OT world view with reality and many other factors cause me to conclude that Paul’s claim (2 Tim 3:16) that the OT scripture is inspired by God is very solid.
As for question number 2, it is harder to reach a really hard and fast conclusion. I can compare the theological background to the various strands of Hebrew and other manuscripts (note: I have almost no experience in the Samaritan Pentateuch). My conclusion (admittedly less solidly based than with question #1) is that the vast majority of copyist errors and editorial misconduct has no impact or relatively little impact on the basic Christian doctrine and world view. The number of soldiers killed in a particular battle and the tense of a particular verb does not impact my faith in God and in the resurrection of Jesus. Even the addition or removal of an entire sentence here and there (a very rare thing in the OT) does not necessarily raise important fundamental questions.
The fact (as I see it) is that God entrusted his words to people. For reasons of his own choosing, he trusted common believers with the task of preserving the inspired texts. God is not in the business of miraculous intervention when the laws he has created, combined with human free will, can act and his will be done. God entrusts his message to fallible people like myself and to those who made copies of the original inspired text. God does not miraculously change a red light to green in order to get me to work on time (although I believe he could if it agreed with his nature to do so). God does not drop notes out of the sky, commanding that we do this and that. He also, it seems, did not force the hand of copyists and translators of the text to produce perfect versions.
It is helpful for us to have separate witnesses to the primitive text. The Samaritan Pentateuch is a snapshot from about 500 BC of the Hebrew text. Similarly, LXX is a snapshot of Jewish understanding of the meaning of the Hebrew text from about 200 BC. To me the differences between such versions gives us a fuller picture of the original than a single text line would, and they also give us a useful measure to reconstruct how much change in the actual text might have happened. Having these disparate texts increases our confidence in reconstructing the original. The more witnesses, the more accurate the overall conclusion.
In the final analysis, unless I find any evidence of a really significant theological, doctrinal or historical question raised by the differences between these texts, I see no reason for this question to undermine my faith in the usefulness of the Old Testament. An example of a difference between the texts is that the Samaritan Pentateuch has the place of worship being Mt. Gerazim. We know from NT information that the Samaritans believed this to be the place of worship. However, I believe that common sense, history and a number of factors very strongly leads us to reasonably conclude that it was the Samaritans who changed the original, not the mainstream Jewish texts. Therefore this difference, though interesting and informative, does not impact my confidence in the reliability of the Old Testament. In fact, in a small way, it actually increases it. So, I am open to you presenting a real theological, doctrinal or historical issue raised by the differences between these texts, but until such is forthcoming, I find this to be an interesting question, but not one which troubles my faith.