We have to be honest, if we owned this card, we wouldn't even attempt overclocking as the ‘out of the box' performance is more than any user would need. That said, we know the Kitguru readers will be interested so we used the bundled ASUS overclocking software to try and push the card further.
The ASUS branded ‘GPU Tweak' software is actually very good, although we found a little interface quirk which might be missed by some customers.
If the user simply adjusts the sliders, only one of the GPU cores will be overclocked. There is a ‘hidden' menu in the software, right next to the ‘Mars II' text. When this is clicked a popdown menu appears showing GPU 1/2 and ‘sync with all card'. This needs to be highlighted in red for the clock speeds to apply to both GTX580's.
What is even more confusing is that the ASUS customised ‘built in' version of GPUz accessed via the ‘info' button doesn't update the clock speeds automatically, like the stand alone version of GPUz. It has to be closed and reloaded for the updated speeds to show. It also won't show both cores, so I had to confirm speeds with the ordinary version of the software.
We increased the core voltage a little to 1088. This allowed us to achieve a core clock of 820mhz from both GTX580's. Memory speeds could be increased to 1,100mhz which translates to 4,400mhz effective. Healthy increases for a single PCB design.
The overclocked speeds helped to push the Direct X 10 based 3DMark Vantage from 41,482 points to 42,937 points. A noticeable increase.
Another increase, this time around 500 points more than with the default clock speeds. Very impressive results.