Rob beat me to it... that was mostly my point, if you ONLY overclock to the 940's 2.93GHz speed then the additional power consumed used over ~4 years is not going to add up to the $266 price difference you pay upfront.
Most Intel CPUs will become
extremely power hungry as you clock them above 3.2GHz... My Q6600 will pull 200W+ of power by itself at 3.6GHz, probably more but I don't have the means to measure CPU-only power consumption.
Power saving technology turned off:
CPU Only Load (measured from the wall)
2.4GHz ~235watts 1.20v
3.6Ghz ~475watts 1.45v
It's no wonder I use watercooling...
And why I most often run with my CPU at 3.2GHz at a much lower voltage.