This request has been added to the tracker:
https://winscp.net/tracker/1502

w0nderer wrote:

Seeing how different servers have different limitations (max simultaneous connections)
being able to set that on a per session basis might be handy

I second that request. Setting the number of simultaneous connections globally in the settings of WinSCP is a bit cumbersome and unfortunately affects connections to other servers that do not restrict the number of connections. Having a way to set (or even better override) the global limit on a per-connection basis as part of the session settings would be a great feature to have.

Kind regards,
-michael

Thanks for your suggestion.
Will see if more people ask for this.

Seeing how different servers have different limitations (max simultaneous connections)
being able to set that on a per session basis might be handy