wingnut771
Honorary Master
Not saying it's the case currently with what you're experiencing, but sometimes people forget that there are occasionally other links in the chain as well. Quite often the drop in speed is at the server side.
I've had plenty of situations where one download would be chugging along at ~10kbps, but starting a second download for something else from another server would use full line speed while absolutely nothing speed related really happens with the first download.
That being said, I've also had times where downloading something to my desktop would not pass double digits kbps, but downloading the same file from the same server to my VPS in the UK would come in at several 100 Mbps. Syncing from my VPS to desktop would then be full line speed again. So either someone somewhere limits those connections, or the direct link takes a slow path somewhere.
All I'm saying, more than one place for things to lose speed.
I think this is where the "best effort" comes in regarding ADSL.