Why is that?  I have a dedicated server in the US for a web server and uploading or download files to/from the server using FTP don't go over 311 kB/s (~3Mbps).  Speedtests give me 50Mbps download.

As a test, if I open multiple downloads then each one is roughly 300 kbps and I can get some substantial speeds with 10 or 15 files downloading simultaneously.  Why can 1 file not go full speed?

Cheers.