there does seem to be a almost linear effect that the higher the Initial speed, the faster and more devastating the age defects are. I asked Ron the photo engineer about this but My knowledge of what happens was not able to ask him a question that he could explain to me.
General rule that I might draw is anything B&W under about ASA 125, little or no visible problems up to 10 years in the open, or 20 years in the freezer. ASA 400 is showing some deterioration after 10 years in the freezer. and the P3200 style films start showing problems after 5 years frozen or not.
My observation to ron was that I got the impression that after a while two rolls, say one Plux-x and one Tri-X after 10 years, the plus x might have a higher useful ASA than the Tri-x. BUT of course I woul dneed more samples and a much more consitant test plan to verify this.