Strictly speaking Hyper Transport isn't related to any DDR2/DDR3 support or the ability to overclock an AMD CPU.
Think of Hyper Transport as a data pipeline. It only has to be wide enough to not dam up the rapid flow of data communications between the CPU and all the other devices in the system.
As Hyper Transport versions have changed the 'pipeline' has gotten fatter with the increased bandwidth (speed) keeping it from being a bottle neck in the system. Increasing the size of the pipeline won't change the amount of data being sent or received. As the MadShrimps article showed only a video task (3DMark06) showing an improvement when the HT was raised from 200Mhz to 1800Mhz and even that was a very small percentage increase. The increase from 800Mhz (HT 1.0) to 1800Mhz (HT 2.0 plus 400Mhz) was an even smaller increase.
In servers HT gets a real workout since it's used to connect multiple CPUs on a server board and servers can be heavily I/O dependent on storage devices which run data over the HT links.
In PCs it's more likely the graphics card (or cards in CF systems) will put the largest load on the HT followed by disk IO.