OCZ Gold Edition, OCZ2G10664GK & Asus M4A78 Motherboard.

In BIOS, under Ai Tweaker, set DRAM Frequency Control to [Manual].

Then set DRAM Frequency to [1066 MHz].

You should also check DRAM Timings 5-6-6-18

I don't have a setting for 1066Mhz

Which is a bummer

It may be listed as @533

I am sorry I looked into the manual M4A78-E and saw there was a setting there. But unfortunately your motherboard is M4A78 and does not have such a setting. You have 400 MHz setting only. Therefore, you will have 800 MHz at most. But depending on the CPU used, you may have 1066 MHz. AM2+ and AM3 CPU support 1066 MHz. What is your CPU ? If you use one of those CPUs, you will have 1066 MHz option. BIOS update may be required.