Jim, one curious issue I've had with outdated 55 is that it has a tendency to get stuck in the holder. I haven't pinpointed why that happens but maybe something is getting brittle. Then I wind up having to disassamble the whole holder on the spot to get the film out, and the frame is usually unsalvageable... what a pain. Apart from that I've had no issues with the quality of the actual negs that do make it through the whole process, and I've used some unrefrigerated 55 that was more than a year past expiration. But it seems to me the chances that they get stuck for one reason or another goes up substantially with time. I bought a new holder, thinking that was the issue, but... same thing with my older 55.
Now, I've had no issues with the old 665 that was refrigerated. But it is a foil-wrapped pack film, of course.
Since I have an 8x10 processor, I was thinking about perhaps feeding the 55 through those rollers rather than trying to process it in a normal holder. Just a thought.