... The most efficient way of transferring large files over a poor connection is probably FTP. FileZilla is one free FTP server, ...
If you're going to install an FTP server, you might as well use the one that IIS includes, since you already have it. But I would recommend rather strongly against it; FTP is
by definition an insecure protocol; since it is defined to use unencrypted TELNET as the control channel, user data (names, passwords) are passed in plain text.
And remember that this is unsupported. :)
I'm not on the WHS team, I just post a lot. :)