I have a 50Mb downstream and 1.5Mb upstream connection (i know

Interestingly enough, newsbin is able to manage a full 50Mb/s - and while downloading at this speed the upstream usage generally hovers around the 1Mb/s mark. Any idea's why sab's upsteam usage is notably higher? I'm using giganews with SSL. I've tried varying the number of connections with no success.
Is there anything I could adjust in sabnzb that might help, or should I perhaps be looking at TCP tuning in the OS?
It's worth noting that my sabnzb pc is freebsd, and the newsbin pc windows 7.