Just to throw in on something I ready earlier in this thread, I'd say that for a general practice with Koha going forward, we should pick a single XML parser that can handle arbitrary schemas, and use that. I would very much like to make Koha not just MARC-agnostic, but metadata schema agnostic, and coding ourselves into a corner now (even for a noticeable performance boost), would make life difficult later. As I think the rest of the thread attests, there are other ways to improve our XML parsing.
If this had already been resolved earlier in the conversation, I apologize for redundancy; I haven't had my morning coffee yet.
-Ian