Is there a default bandwidth limit on FTP or SFTP?

Hello all, I have a pretty decent connection to my xserves (3Mbps w/10Mbps burstable), however if I am uploading to one of them, I get about 20Kbps. I am on cable internet here at the house, and when i run a test on speakeasy or some of the other bandwidth testers, my connection consistently gets approx. 4800Kbps down and 360Kbps up. So I was wondering if FTP, SFTP and/or ipfw have some type of default bandwidth cap that I can check on and adjust? I have a Gigabit switch at the xserves, so I don't think it's a hardware issue. thanks for any help, Jim