Use the speed tester on this site and post a link. It uses both single and multi thread and can be quite good at showing up issues with congestion. I assume you have checked your modem connection stats to make sure there is no underlying issues with the connection itself?
I cannot get to the speedtest on thinkbroadband it says I have not been activated even after changing my password.
Sky have sent an engineer out to me 3 times and tomorrow, Wednesday 17th May, they are sending another engineer. First visit they changed my master socket to a Mk4 and discovered the fibre board in the street box was faulty, it was replaced, speed dropped again to create visit 2, by this time I had been sent a new router by Sky, The line was reset again, a week later speed had dropped again and the third visit arranged, that time the cable that runs from the front door connection box to my master socket was replaced, speed was good again but as before only lasted a few days. The last 3 days my speed has been around 20Mbps and this was the same on thinkbroadband speedtest without me being able to signin. Now waiting to see what the engineer will say about this tomorrow.