I've pretty much stopped buying eBay film and paper. I got some good stuff and some not so good stuff that way, and just decided it's easier to learn to work with fresh stock that's in current production and go with that. I think that even if I shot 12x20", I'd probably pass on this and just shoot Efke PL100 (as I've done with 11x14", which I do shoot).
I agree with David on this. Even if the Super-XX has been frozen and kept in perfect conditions it will have developed a lot of B+F since 1990. A couple of years ago someone gave me a few sheets of film from the same year, which was for sure frozen since it was purchased, and it had developed a B+F of about .45 over normal. It was usable but definitely not something I would recommend for printing with slow alternative processes.
Personally I would much sooner put my money on a film like Efke PL100, assuming it is fairly fresh. Caveat here is that Efke develops B+F very fast if not frozen, so that even film that is only one or two years old may have a lot of B+F.