We set the Power Limit at the maximum 110% to check out the overclockability of our Zotac GeForce GTX 660.
It is impossible to increase the GPU voltage of a GeForce GTX 660 card, so we only managed to raise the GPU clock rate by 90 MHz from its default 993 MHz. The memory chips could be overclocked by 660 MHz:
The resulting GPU and memory clock rates were 1083 and 6668 MHz, respectively.
That’s not much of overclocking, considering that Radeon HD 78xx and 78xx cards can reach 1200 MHz in GPU frequency and 7000 MHz in memory frequency, even though the boost frequency of our overclocked GPU was as high as 1175 MHz:
By the way, take note that the card’s temperature didn’t change after overclocking, and the peak speed of the fans remained the same, too. That's another proof of the highest efficiency of Zotac's original cooler.
We measured the power consumption of our testbed equipped with different graphics cards using a multifunctional Zalman ZM-MFC3 panel which can report how much power a computer (without the monitor) draws from a wall outlet. There were two test modes: 2D (editing documents in Microsoft Word or web surfing) and 3D (three runs of the Metro 2033: The Last Refuge benchmark at 2560x1440 with maximum image quality settings).
Here are the results:
The system with the new GeForce GTX 660 is obviously the most economical here, requiring less than 400 watts. The Radeon HD 7870 GHz Edition needs 25 to 30 watts more, which is not a big difference. And the GeForce GTX 660 Ti needs 35 watts more than the GTX 660. The systems with different graphics cards need about the same amount of power when idle. Overall, modest power consumption is typical of graphics cards of this class.