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Too easy, to reach 3GHz you'll have to raise your FSB to 300MHz. That will put your RAM at DDR2-600 speeds. So any RAM rated for DDR2-667 speeds will work fine. You can find DDR2-667 for as low as $120 for 2GB on newegg 8O
Actually, you need 333FSB to reach 3GHz on a E4300.
But like you said, and 667 RAM kit will work.
Oops, you're totally right