I have a server that has a 100 Mbps connection, but (perhaps due to latency) I can only get 450 kBps connections to it. I can, however, create multiple connections until I've saturated the link between myself and the server. In the old version of WinSCP, I could transfer up to 9 files concurrently, each of which would max out around 450 kBps for a total of about 4 MBps. With the new version, it tosses all the files into one transfer and the total speed is just 450 kBps. If I select one file to transfer at a time, then I can get it to display the previous behavior, where it produces multiple concurrent file transfers. I've experienced this with both the SCP and SFTP protocols on Win10.
Also, I'd really like to see a higher max connection limit.