What is Stunnel?
The Stunnel program is designed to work as an SSL encryption wrapper between remote client and local (inetd-startable) or remote server.
It can be used to add SSL functionality to commonly used inetd daemons like POP2, POP3, and IMAP servers without any changes in the program's code.
Its architecture is optimized for security, portability, and scalability (including load-balancing), making it suitable for large deployments.
What Stunnel basically does is that it turns any insecure TCP port into a secure encrypted port using OpenSSL package for cryptography.
It’s somehow like a small secure VPN that runs on specific ports.
SSH SSL/TLS Tunnel
is a secure shell (ssh) wrapper in SSL encryption on openssh service and dropbear service.
SSH itself already has encryption like SSL, but we try to wrap it again to make it more secure.
With SSH that supports SSL / TLS connections for tunneling running on port 444 for openssh and port 80/443 for dropbear.
The speed gained will not decrease between SSH supporting SSL / TLS and not supporting SSL / TLS.