I am confused about what you are trying to acheive (not that I can influence or help, just curious).
My understanding is:
1. that you have a need to FTP, sometimes, large files (how big?)
2. that you would like to do this mostly during business hours (which are approx 50% off-peak and 50% peak).
3. that you wait until peak time because ....
The .... is where I am missing something. Have you tried to FTP a large file during off peak and had it slow? Fail? Something else?
Unless there is something technical preventing you, follow Nike's motto, until you run out of the 48GB
