It would be nice it WinSCP will have ability to use UDT protocol for transerring data.
UDT (from sourgeforge) is UDP-based reliable transport. It has own congestion alorithm, and is using all available bandwidth and is latency-insensitive.
In my experience, typical trasnmition rate is 95% of bandwith with latency <1ms, 90% on latency 20ms, 75% on latency 150ms.
Example imlementation is hscp (on sourceforge)
Suggestion is that you will implement in WinSCP hscp client part, that will be able to connect to server from hscp project.
hscp is using scp for authentication but transferring data through udt. Data transfer is not secured by SSL.