A couple of correspondents (so far) have pointed out, in relation to the sagas business, that Beowulf was not influenced by the Norse sagas, since it was, apparently, written 300 years earlier. Which is a fairly convincing argument. Also that Sir Gawain similarly predates the sagas and is 'an alliterative Arthurian romance'.
Well, there you go, see. I should have known better than to believe what I read on the internet. But how reassuring to learn that the readers of the GOB are such a literate and well informed group.