I'm thinking about a different route. I don't know what kind of "good" information can be contained in a +65K line Excel spreadsheet. I don't think people looking at that data could glean any meaningful info. Try to go back to your customer and find out what they're using this for. You may be able to deliver a better solution thru an SSAS report or some kind of Excel Pivot table that reads from an SSAS cube.

If you're just dumping informational rows of data, try using a different format, such as CSV. Then the user can use some other tool (Access, etc.) besides Excel to view the data. But I would still consider the reason for the report request.