I just found out that if I lower my GPu speed by 20%, I can save like 35% of electricity.
While this could be possible if you're pushing you PSU or cooling to the limits it should not happen that way. clock speeds more or less control wattage usage in a linear fashion - double clock speeds and double your wattage. Voltage needs to be squared when control wattage usage. So 50% voltage is 0.5x0.5 = 0.25 or 25% of the wattage.
So if you take a card that normally runs 1.0v and clock it down to 0.8v but keep the same clocks, you should be lowering the power for the core by 0.8x0.8=64% of previous core usage. Of course other card components will still use the same power like the memory and the fan (assuming same RPM).
