In that case i would try disabling the server in your client for a minute and going and registering for a free usenetbucket account (if you register with facebook you get 20GB free for 7 days) and do the same thing use the 50 connections but also use SSL, usenetbucket allows it on their test account and just compare your speed between the two. It should let you know if its a problem with your current provider or if its something with your connection.
Also a general rule about the connections once you have it maxing your connection speed you should reduce them until you are using the minimum amount needed to max it + maybe 1 or 2 extra. This is because they increase overheads and its generally a waste.
Have just tried that and now it is reaching speeds of 19Mbs, using 50 connections, port 443 and SSL, so it is probably something wrong on my end?

but yeah, in the speed box it shows 19.1MB/s.