Thanks. It seems the memory isn't much of a problem now, but the time is the greater issue. Our users don't want to wait 5-8 minutes for an excel export. I'll have to make sure our version of PHPExcel is at head, then go over your recommendations to see if I can make it faster.
You're doing a fine job with the script, and if there are some improvements I can make to make it faster I'll let you know.