a lot depends on how close you are to the server, but alot depends on the quality of the test and how well it is writen as well as the backbone providers that carry the data to you.
the same thing happens with my ISPs speed test i get a lower result with them and a much faster one with testmy.net.
a 256kbps upload is not going to work for streaming a 700mb movie file.
Your eather going to have to get a decicated server, VPS, or a shared host with a lot of bandwidth. http://ixwebhosting.com you can get 1tb of bandwidth for 4buck a month.