Here's a mock source-criticism analysis of the "T" and "PJ" redactions of the "War of the Ring" traditional narrative. Interesting, but I think the author neglects the possibility of an earlier "S" redaction or "UT" collection of sources which might explain a number of common narrative elements between the received texts without direct communication between the two redactors.

As for the kerfluffle about who the Rohirrim are supposed to be, I'd go with Goths-with-stirrups, myself. They're early-Germanic nomads living on plains that had once been occupied by the Fallen Empire, but now exist in political independence-but-culturally-influenced. Maybe the Avars? I don't think they were Germanic, though...

Via Professor Bainbridge here and here.