Thanks for the quick replies!
I wouldn't classify my filters as having heavy use because I was a graded paper only user up until about the mid-1990's. Therefore, at most my 6x6 set saw about 4 - 5 years of what I'd call low-to-moderate use. For the past 13 years or so, both sets have been stored in a cabinet drawer devoid of any light, in their respective original spiral thingy in the box, and in my house. I wouldn't imagine anything related to storage being an issue.
@Michael R 1974 - the 00 and 5 filters in my sets are as you describe. I must have a later version rather than an earlier one.
I think I'll proceed as pentaxuser suggested...I'll grab a known neg and print it through the various filter strengths that I would normally use, and then simply compare for expected contrast differences.