There is bigger factors that affect energy consumption : voltage, core & mem clock, PSU efficiency, other component consumption like CPU and RAM.
Yep, this. The only thing that can affect my power consumption is lowering the actual settings of the GPU.
Lowering the voltage: Your #1 method of cutting power use. Also helps a ton with temps! The lower the voltage, the less power you use. Problem is you need a voltage unlocked GPU. Also, the lower the voltage, the less you can OC the GPU, so you have to find a balance.
OverUnderclocking the GPU Core: Your GPU Core is the biggest draw of power on the GPU. Reducing that draw makes a huge difference. It's not exact, but typically, at the same voltage, a 10% drop in core speed will also be a 10% drop in the core's power consumption. Also, a lower core clock will let you undervolt farther, reducing consumption even more.
Memory Clock: LTC mining uses high memory clocks, and lots of memory activity. BTC Minging (when it used to be on the GPU) used extremely low memory clocks, and almost no memory activity. Because of this, LTC mining uses quite a bit more power. I think there was a 40-50W difference on my 7970, but I can't remember the exact numbers. Anyways, lowering the memory clocks will also reduce the memory usage, which isn't a huge deal, but still a factor.
PSU: PSU
inefficiency is also a HUGE factor. For a 4x 7950 GPU rig, a 88% efficient PSU and a 93% one can be a difference of 50W or more from your draw at the wall. That's also 50W of heat that your PSU doesn't have to dissipate, heating up your case temps or your ambient temps.
And lastly: Rig hardware: You don't need a huge gaming CPU for a mining rig. I think it's crazy when people throw an OC'd i7 or a beefed up AMD FX 8-core CPU on a mining rig. there can easily be a 100W difference between an OC'd FX-8350 with power savings off, and an underclocked Sempron 140 with all the unnecessary BIOS features turned off (sound, firewire, 2nd SATA, wifi, etc).
