How can I speed up my lftp uploads when I'm mirroring?

Here's my script:

#! /usr/bin/bash
set -xe

local_path="${1-./}"

lftp -u user,pass host << EOF

set ftp:ssl-allow yes
set ftp:ssl-protect-data yes
set ftp:ssl-protect-list yes
set ftp:ssl-force yes

mirror --reverse --continue --parallel=5 . "$1"

quit
EOF

Is there anything I can change/add to the script to speed up uploads? There's a lot of neat tricks I found for speeding up downloads, but I can't find anything beyond what I already have. I can connect to the host over FTPs or SFTP. All things being equal, would one be faster than the other? I am trying to upload a very large file, not a bunch of little ones. Therefore, I don't think the parallel option can be used.