If you are running multi threaded applications you need to be in unganged mode, this is the fastest way of running the system.
ganged mode is 1x128bit dual channel
unganged is 2x64 bit dual channel
Ganged mode is often the default BIOS setting and is considered to be better for single-threaded applications, while unganged can provide better performance in multi-threaded applications. Some initial testing was performed in both modes, with results indicating that neither really provided a large overall advantage. Unganged mode offered a slight edge in applications and games, while ganged mode took a few wins and provided much higher memory bandwidth scores in the Synthetic Sandra VII benchmark. So, while there may be specific applications for which one mode provides a real advantage over the other, overall, at least in our tests, effects are minimal.