I personally found my RAM needs a lot more voltage and overclocks a lot less willingly when I have 4GB of it in there, but it depends on how you're getting that CPU clock. I mean if your FSB is such that you could underclock your RAM to sync with it or only slightly overclock your RAM, it shouldn't be a problem, although if I install 4 GB of my current RAM (OCZ Platinum XTC DDR2 PC6400 blah blah blah) it can barely clock past 830MHz.
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