I have said it before, but it is worth repeating, if you want to transfer a large file over the internet between two persons, Bit Torrent is still a good solution.
You obviously need to encrypt the data before sending it, but 7zip should sort that out for you, you then just create a torrent and send the torrent file over, and seed the torrent until completion.
As long as the file is securely encrypted and both sides terminate the torrent as soon as the intended recipient has the file, the risk of data leakage is minimal.