|The Core 2 Duo comes in either 800MHz, 1066MHz or 1333MHz FSB versions.|
- if you have the 800MHz FSB version & you're NOT overclocking, all you need is DDR2-400 or DDR2-533/667/800 underclocked to DDR2-400 speed
- if you have the 1066MHz FSB version & you're NOT overclocking, all you need is DDR2-533 or DDR2-667/800 underclocked to DDR2-533 speed
- if you have the 1333MHz FSB version & you're NOT overclocking, all you need is DDR2-667 or DDR2-800 underclocked to DDR2-667 speed.
In other words, if you already have DDR2-667, you won't gain anything by replacing it with DDR2-800. And if you're gonna add RAM to increase your total memory amount, you can get DDR2-800 but it will downclock to DDR2-667 speed. Even so, your DDR2-667 *probably* needs to be underclocked anyway.