what i've learned from an overclocking forum i also belong to is that the important thing isn't the rated speed of the ram (remember, plugging ddr400 ram into your mobo doesn't mean that it's RUNNING at ddr400 speeds) but rather what actual memory chips the stick is running.
I've heard the "D9" ram is rated anywhere from ddr2 500 to ddr2 1000, for example, but any of the sticks can be run ~450mhz, and the only difference on the 1000 sticks is that they have heat spreaders, or even water cooling pipes.