>Naomi, I have one other link for you to look at. I have not used this particular process but Craig Boyd's stuff always just works for me. Bo Durban worked on it as well and they are both gurus for sure. This may be more what you need because of the number of rows you are describing:
>http://www.sweetpotatosoftware.com/blog/index.php/2008/09/30/using-excel-2007-file-formats-in-vfp-9-0/

It was an urgent problem and at the end I just loaded both files into SQL (locally) and compared them this way. I would need to discard that data locally as I already moved the difference into our Azure DB.