Clock speeds and timings can be faster with overclocking modules. Kingston, for example, makes PC3500 modules for up to 433 MHz.
You can start out with special tweaking modules that exceed the DDR400 standard and offer particularly high settings for clock speeds and timings. The modules are available from Corsair, Geil, Kingston, Mushkin and others as PC3500 or PC3700. While standards by these names don’t really exist, the names indicate how much the modules can be overclocked.
But DDR RAM doesn’t really spread its wings until it’s installed in dual-channel motherboards that add together the memory bandwidths from two DDR modules. These mainboards sport Nvidia nForce 2 chipsets for AMD CPUs, or Intel 7205 (and, in the future, 865 and 875) chipsets for Intel processors.
There is one catch - you always have to have two memory modules. BIOS often puts the brakes on the RAM timings so that the system remains stable, and that’s where most of the optimization comes in. In fact, RAM manufacturers such as Corsair and Geil even sell matched pairs of memory modules as a bundle especially for dual-channel systems.