I think it's got to do with the difference between memory voltage and memory controller voltage. For a reason that I can't remember, changing the voltage in PBE and WattTool only affects the memory controller voltage, but the memory controller voltage will continue to supply the memory with the standard 1V voltage. Only way to reduce memory voltage directly is by setting a negative offset in the BIOS directly by way of a HexEditor. You can search for references to this by @Heliox
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