About the upload speed, I remember that FileSonic's FTP server routing is much different with other file servers.
When I did traceroute to their file servers (sxxx.filesonic.com), the routing was just like the ones of other file hosts using WebZilla.
However, there are a lot of "Level3" nodes in FileSonic's FTP server routing, which are not present in their general file servers' routing.
I have saw many new file hosts, such as SlingFile, choosing WebZilla as their DC but get very bad FTP upload speed.
So I guess it's the secret how FileSonic won the market.
When FileSonic stopped file sharing service, they removed their FTP servers quickly.
I think that special connection cost them a lot.