DDR2-1066 is not DDR2-800 that runs at 1066 by overclocking.
DDR2-1066 does indeed have a SPD byte which will identify it as such when the proper conditions are met - that means it's not overclocked DDR2-800. It really is 1066 RAM - it may have been made by the same process as a company's 800 RAM, but it doesn't leave the factory without being changed from the 800 by having the SPD set.
And overclocking, traditionally, refers to modifying related BIOS settings to create something that doesn't otherwise exist in the BIOS. That's not what's done with 1066 RAM unless the board specs say "1066 OC". I have a setting that is proper in my BIOS for 1066 RAM, just like I have one for 800 and 667 RAM. I'm not overclocking at all by putting in 1066 RAM and setting the motherboard to the same.
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If you have a motherboard that supports 1066 RAM, then first set the DDR voltage to match the specs of the RAM you purchase, then it may come up as 1066 automatically. If not, then set the speed as 1066 in the BIOS manually.
Once the POST sees the RAM as 1066, it means it's found the spd for the 1066 mode and CPUz should show it as both a 1066 model number and the spd for it. If the POST - when the system boots and shows the RAM speed - shows 800MHz RAM, then CPUz will only show the spd up to the 800 mode.