Well, I can't answer this as I have never run 8GB, but you *should* be able to achieve a good overclock but you will need to be very careful with timings, and it will need decent vNB, and it has to be fully compatible with the P45 chipset, I'm not sure if that particular ram is or not, but it should be possible. Look to some of the guys running 4GB and base your template for 8GB off theirs.
You should also be able to do better than 3.2GHz on a P5Q-D, 500 FSB has been done with a quad, I think Leeghoofd has done it and others too.
Have you set any voltages at or around that level? perhaps vPLL and vFSB? Also OCCT is not the tool you want to be using to measure voltages. I'm quite sure the bios/board doesnt have the capability to detect vPLL, vFSB, vNB or vdimm, so who knows what those voltages are.
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