Are there limits on number of variables / calculations
 

Our company produces financial statements for clients using an Excel workbook
that has numerous worksheets relating to financial years. Each sheet is
populated by extracting data from our SUN (Systems Union) accounting
application using their 'Vision XL' add-in. VBA macros do a lot of the grunt
work and have numerous variables, including some relating to named ranges
that are referenced in the multitude of formulae within each sheet.
While these financial workbooks have been working fine over the last years,
our client information has grown and obviously financial years are added
annually and the workboks for some of our clients have become rather large.
My management is concerned whether there could be any limitations in
Excel/VBA that might cause them to stop working or give unpredictable results.
Does anyone know of any limits on the number of variables / calculations (or
combination thereof) that we should be wary of?
Many thanks in advance.

Keith Carter