You can start by determining the ASA and the film base fog value of the different films. I'd start with the newest one that you have the most of. You can try different developers to see which gives you the least fog. I would photograph Zones I & VII on the same sheet of film, starting at the manufacturer's recommended speed, then 1/2 and 1/4 the film speed (ASA). This will give you three sheets of 4x5, then I would make two duplicate sets to vary your developing time from the recommended time with the developer, then 1/4 less and 1/2 less (or more) of the time. Read the densities with a densitometer and determine which Zone I exposure gives a density of 0.15 over the film base plus fog. That sheet is your film speed rating. Then read the Zone VII density of this sheet with the different developing times and determine which time reads 1.15. That is your developing time. It will probably take several tries to zero in on it.

I suspect you'll find that the zone I density is probably lost in the film base. I'm presently doing this with some T-X 4x5 which expired in 1988, developing in HC-110. I have over 1000 sheets of this that I've kept frozen. The film base is over 0.3. I haven't been able to get a Zone I exposure to register above the film base + fog, so I'm in the process of trying for Zone II. I'm also going to try it with Rodinal to see if the fog is any different. I'll post my results when I've figured it out.

Yes, it's time consuming but I would do this before visiting the dumpster.

L