It could be a set of uncompressed media files. I just recorded a friends album, and 16 tracks were like 800 MB, so it could be anything really.
But back to the question at hand. Minamr, you could always just set your FTP to start when you go to bed or to work or something. It will naturally tie up your phone line for that period of time, but it works. Get yourself some Zzz's, FTP and you'll be good.
Just a thought