I have a lot experience in Excel files, specially with huge amount of records, for 3 years last in my job as Business Intelligence Report Designer and Generator , I have populate all company transaction , with 40 branch, each branch have at least 2000 record transaction in a day. So for 1 month , we have around 2 million records in 1 Excel file, with a lot of worksheet , like Daily Transaction summary , Weekly Transaction summary, Quarterly , Monthly , Yearly. We also have Top Ten, Bottom Ten for many category.
For some summarize data , I have to upload to our company website for at least 10 principal, and 100 major customer. I have very fast Internet connection around 6 MB/s, so for uploading data process will be more than enough.