NOTE FOR MODERN OPERATING SYSTEMS
Windows XP used to have issues running fast over higher latency connections hence the whole "Tweak" business grew online with tools like this and many others. More recent versions of Windows, as well as Linux and OSX and mobile devices do a good job of automatically optimising connections, and "tweaking" is just not required or in the case of Windows, even particularly easy to do. Modern broadband connections tend to get used by many services at once and tweaking a connection for higher top speed was always about optimising a SINGLE transfer.
With the advent of consumer 100 to 1000 megabit and beyond connections, speed tests (which were used to "test" tweak effectiveness) now need to run multiple streams and this obscures any change in single transfer speeds.
If you work in academia and have need for high speed single-stream transfers over long distances you can find better guides online for TCP modifications that can increase the speed of such transfers beyond the already high limits the modern OS imposes - but usually these come at the expense of the reliability and flexibility of local transfers.
Too Long - Didn't Read : the tweak testing tool is retired