Runing the memory at DDR400 with the CPU at DDR333 might not give you a performance lead. But the last guy mentioned overclocking...say you overclock your CPU bus to 190MHz. Well, running your CPU at DDR380, it would be handy to have memory that doesn't crap out at DDR380. At what's more, your NEXT CPU might be a "400MHz bus" Barton. You don't really want to upgrade your memory every time you upgrade your CPU, now do you?
<font color=blue>Watts mean squat if you don't have quality!</font color=blue>