A client who's got 70,000 rows in a spreadsheet needs to learn about Microsoft Excel lists. Especially when used in conjunction with Microsoft SharePoint (which is a thin wrapper over SQL databases and file-synchronization technology), this represents a much more intelligent way to manage this data.

And if you don't want to go that way, well, the client undoubtedly has Microsoft Access, and it is easy to define a spreadsheet list which links directly and invisibly to that database. They won't have to change their data, formatting or basic work-flow.

(Eeeee-yuck! I've just caught myself recommending Microsoft, and I didn't say one thing about Perl!)   ;-)