Basically, the registry settings described simply changes your TCP window settings.
TCP transmits packets and expects acknowledgement from the receipient, and if its not obtained, it retransmits the packet(s).
Windowing is a mechanish whereby TCP judges how much data/packets that may be sent at one go, without waiting for acknowledgement.
This varies with your connection, latency etc.
Hence the change described positively affects, and you may notice greater speeds.
However, In any case, its never possible to exceed the capacity assigned to you by your ISP.
regards,
Nitin.