Leolaia:
I found your reconstruction of the textual history of Mt 10 // Mk 13 // Lk 21 // Jn 14 quite compelling.
On the relationship of the Pauline letters with the "sayings of the Lord", I will try (perhaps not succeed) to address your objections (following your list):
1) IMO the difference (formal correspondence not referred to the Lord vs. non-formal correspondence referred to the Lord) points to a different kind of tradition transmission (pleonastic, sorry) as far as Paul is concerned. That is, when Paul explicitly refers to "the Lord" he never writes anything similar to the Gospels, even though analogous ideas may be present in another form in the Gospels as we know them. This may mean that the knowledge of "Jesus' teaching" Paul has through the Hellenistic churches is quite independent from the knowledge he has of literary material which was later presented as "Jesus' teaching".
2) The argument that Paul mentions the Lord only when and because he paraphrases sounds weak to me. If authority is at stake, the challenge would be far better matched (especially in a mostly oral context) by quoting formally ? if such a thing could be done. If Paul does not quote the Lord formally (from the standpoint of Gospel tradition), it is because he cannot do it ? or because the Lord?s sayings he refers to are known in a different form in the community he addresses.
3) The author of EpJames would also have made a better point in his own context had he quoted Jesus, if the material he uses was known to him as Jesus? words (my provisional conclusion: he knew the material, but not as Jesus? words).
4) About Rm 13:7 I must correct my hastily classification: actually there is a tenuous but important verbal link to Mt 22:21//, the characteristic use of apodidômi (taxes are something to be given back, which is not a very common and natural thought as far as I can guess).
5) I really wonder if 1 Th 4:15 can be seen as parallel to the ?first and last? sayings in Mt 19:28ff or Lk 14:20 at all. This seems slightly farfetched IMHO. If it is not, this refers to a "saying of the Lord" which is altogether absent from the Gospel tradition. (But this can also mean extatic revelation.)
6) The fact is that the Gospel-like formula in 1 Co 10:27 is not mentioned in the context of mission such as in Luke 10:8. The possibility exists that this is in fact a Pauline expression which Luke brought into a new context (no parallel in Matthew), and that the parallel in (final) GThomas (also in the context of mission) is subsequent to that.
7) There is no doubt that the paraenetic sections of the Pauline letters lean heavily on non-pauline material, especially church tradition. However, the difference between formal analogies not referred to the Lord and non-formal analogies referred to the Lord may indicate that in his sources most of the Gospel material was not yet ascribed to Jesus...
I'll see if I can find something on that (and on the Kingdom of God issue) in my library tomorrow...