Overclocking is not an exact science. When it comes to overclocking headroom, every GPU is different. And just because your friend's GTX 580 hit 1000MHz doesn't mean that yours will, even using the same settings and hardware. Many factors can influence what a graphics card is capable of, starting with the unique capability of each GPU. These factors may also include complementary components within the system, but we find the primary influence is the type of cooling employed on the graphics card.
We expect the type of consumers interested in these cards want to get the most out of their investment. While it may seem excessive for some, raising the frequencies on pre-overclocked cards should drive even more pixel pushing ability than already available. It merely requires a bit of effort and patience to massage frequencies and voltages while achieving stable operating conditions. We've taken that step for you in order to show the possible gains of manually overclocking the GeForce GTX 580 and these cards. For this testing, we employed MSI's Afterburner overclocking utility since it's free, widely available for download, and compatible with any brand of graphics card.
Although the Gigabyte N580UD comes with most conservative overclock of the three cards, it proves to have the most overclocking headroom by an ample margin. With voltage at 1.15V on the core, we managed a blazing 1005 MHz GPU speed and 1265 MHz memory frequency. That equates to a 26% overclock over the card's rated speeds of 795 MHz core and 1002 MHz memory.
The MSI GTX 580 was no slouch either. It went from its rated speeds of 823 MHz core / 1069 MHz memory to frequencies of 940 MHz / 1145 MHz. These settings give you a 14% GPU overclock and 7% on the memory.
Zotac's Amp! Edition offered overclocking headroom up to 925 MHz core / 1250 MHz memory. If not for the blistering speeds hit by the other two 580's, we'd be a little more excited. But the lesson learned here is that NVIDIA's latest batch of high end Fermi GPUs will award its owners with more performance if they take the time to tweak the settings.