Virtualmin backup to FTP site

We backup our Vrtualmin servers to (horrors) a Microsoft Server which has excess disk space. The Fedora 8 server and the MS Server 2003 server are on a gigabyte switch. When I run ftp from the console on the Fedora machine, the backup files transfer at 57 megabytes per second. When I let Virtualmin do it via scheduled backup the files transfer at 245 kilobytes per second. This is currently acceptable but hardly optimal and will become a problem in the future.

Explanation?

Mike