Thanks for the help everyone. I think I'm going to order the 5qt. I also emailed a few people selling them on ebay, some good prices there, and the responses I got back are in line with a bunch of other sources.
It looks like the pan should be the 12 inches I want inside and about 2-7/8" tall. I think that'll be perfect for what I'm looking for. If that's right then it looks like they basically use the same dimensions as the TK rondeau I have which would mean the lid would fit.
If those dimensions are right that also means it will have a true volume of about 5.6qt which is really nice. Considering you can find a bunch of places to get a brand new non-second of these for $200 it seems like an awesome option.