Sean,
I bought 50 sheets of Astia with an expiry date of 1999 from Freestyle, which they said was cold stored. the only thing "wrong" with the film was that it needed a warming filter (like an 81B) to make the film have a normal color balance. I think David is right, I'd give it a try as a regular transparancy, perhaps rating it at 32-40 and using a warming filter. An 8x10 on a lightbox is awesome!
BTW, I once developed a sheet of transparency film in pyro by mistake. the pryo and fix seemed to have no effect on film, when all was said and done, it looked unexposed. C-41 cross processing would be a better bet.
Tom