When I download an ISO image (which is around 4GB) from the server I get around 70MBps of download speed (which actually is the maximum upload speed of that server) with FileZilla client. However, if I download that same file using WinSCP I only get around 30MBps.
I've read at WinSCP FAQ that unchecking "Optimize connection buffer size" has helped some people to improve their speeds, however this checkbox is checked but disabled (greyed out) when I use an implicit FTPS connection, so I guess that setting only applies to SFTP and SCP connections.
I've also tried some other releases of WinSCP (versions 4.3.3, 4.3.9, 5.7.0, 5.9, 5.11, as well as the latest 5.14.4RC), but almost all of them seem to behave exactly the same. Curiously enough, the oldest one (version 4.3.3) reaches around 40MBps, which is 10MBps higher that the newer versions of WinSCP, but still well below FileZilla client.
Just to verify if the client was the limiting factor, I've used also cURL to download the very same ISO file from the same implicit FTPS server, and I'm also getting speeds around 70MBps (just like FileZilla client). That suggest that the client seems to be the key in this issue.
Is there anything I can try to improve the download speed when connecting to a FTPS server using WinSCP?
Thank you very much.