Difference why those Speedtest on Web is, they mostly fool u and use alot of connections to saturate ur Line just like torrent is doing it, While downloading a file without a DL-manager is using just 1 connection. But normally u should be able to saturate ur Line with just 1 connection, if it doenst ur Line is crap
I was having this issue as well.. Turned out the issue was all the additional entries in my Hosts file from an anti-spy script I ran some time ago. Once I reverted the changes and rebooted my PC all was well again.
Everything was fine until Windows updated to a new build. Then I noticed same issue again. I just reapplied the TCP Optimizer tool and again it fixed it. I guess I'll have to reapply everytime Windows updates. I did submit feedback to MS and included what registry changes TCP Optimizer creates. Hopefully they'll fix whatever is causing this.
For those having download speed issues. On my computer repair customers that have download speed and slow website loading issues on windows 7 has usually been repaired by removing from their networking adapters (properties on wireless, LAN, etc) everything except "Client for Network.." and IPv4 and uncheck IPv6. I have seen like 10 items listed there all interacting with your networking potentials, Microsoft filter this, filter than, this and that and the Microsoft File and Print sharing server (where they have no intentions of sharing any files over the network or a printer), I remove them all and leave just what the user needs to have a smooth internet connection. Of course this is for windows 7, I dont have Windows 10 and haven't troubleshooted the first Windows 10 machine from any of my customers yet so I can't tell you if by performing this step under Windows 10 if that will solve your speed connectivity issues.