Is there a rule of thumb as to how big an accumulation of data one needs before
it becomes better to use Access rather than Excel sheets?

I have workbooks with say 100 sheets of pretty much fixed data in a 100x50
matrix, and then several sheets that actually do calculation on that data. Each
day I add another sheet. At what point is it worth the effort to split the
thing into an Access database, and an Excel workbook that analyzes the data?

It works fine now, but continues to get slower and slower to load and store.

Thanks.

Bill