In addition, you cannot trust those speed test sites. They can vary greatly in results and none are entirely accurate. I've seen my 10mbit downloads show up on them from 2mbit up to 20mbit. Uploads vary just as much on those speed tests.
Second, keep in mind that your speed on those may not be kB/s, but kbps. 280kbps means you have a maximum upload of 28-35kB/s. Then, as mentioned, it will depend on what other internet things you have going, speeds others can download, etc. That and DCC isn't really a great protocol for file transfers... you will generally get faster speeds up and down from just about any other protocol.
