how to use hpn ssh with sftp command
MacPorts would install sftp in /opt/local/bin/. You can test against the OS installed /usr/bin/sftp.

The OS installed zip uses gzip compression by default but can be configured to use bzip2 (with the -Z option) which should give you better compression. I would split the 100GB of files into smaller archives.

Next, consider using tar or xar to create your archives. tar with xz should give you the best compression,xz should already be installed by MacPorts. Of course these suggestions depend upon the tools available on the remote host.