For the stuff which expired in 04 I'd just try shooting and developing a roll as normal.
I had a roll of generic colour negative film of similar vintage which I finally got around to using last year, aside from the colours being a bit muted (which might have been a characteristic of the film and not age-related) it was absolutely fine. It hadn't been stored particularly carefully other than keeping it out of direct sunlight or extremes of temperature.
Personally I wouldn't cross-process slide film, it's getting hard to find. Just get it developed normally and either scan it or buy a projector, you can find good quality ones for not a lot of money now.