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I just got this board along with E6600 G0 and 4GB (4*1GB) Crucial Ballistix and no matter what I do I can't seem to get it stable with the memory at the stock 1066MHz.
What I've done is underclocked the memory a bit and am running tighter timings instead, awesome board otherwise though.
You tried updating the BIOS to 5005 as earlier ones were not great with 1066 memory. If you have you could always try loosening your timings if not already tried, as with 4x1GB might strain board a bit.