OverclockingObviously each individual card of any model can react differently when overclocked but we tried to push all the cards in our possession so as to be able to observe any generalities. Note on this subject that the reference, Asus, EVGA, MSI and Zotac cards were supplied to us by their respective manufacturers, while the Gainward and Gigabyte cards came from in-store stocks.
In an open test system, we used Furmark to load the cards to a maximum to ensure stability by increasing the clock in 25 MHz increments, without changing the original GPU voltage. Next we looped Crysis Warhead to validate the overclocking as, generally speaking, this exercise is more demanding than Furmark.
Note that GDDR5 memory has different mechanisms for the detection of errors that mean that although the memory remains stable when overclocked significantly, it does lose a lot of time to repair the associated errors, either by returning the corrupted data or recalibrating frequencies. Given that the Fermi GeForces struggle with a high memory clock, we didn’t overclock it.
Here are the clocks that we obtained:
Note first of all that the GPU voltage isn’t fixed and can vary from one sample to another. This gives NVIDIA more flexibility when it comes to validating its GPUs at a given spec.
The GeForce GTX 580s generally clock up to 850 or 875 MHz without too much difficulty. Only the EVGA Classified and Gigabyte SOC went up to 925 and 900 MHz respectively without any difficulty or modification of the GPU voltage. Given their high base clocks, these only represent 8 and 5% clock increases respectively. Although, also overclocked to a relatively high level the MSI Lightning wouldn’t go beyond 850 MHz and remain stable, which translates to a small gain of 2%.
The cards with reference clocks, or clocks close to those of the reference card are often those with the highest overclocking margin, the factory overclocking eating into it even when GPUs are handpicked.
For information, we observed the performance of all the cards at their original clocks and when overclocked in Crysis 2, at 1920x1080 DirectX 11 Extreme:
In comparison to the clocks of the reference card, factory overclocking allows for a gain of between 1 and 9%, with the EVGA and Gigabyte models out in the lead here of course. Once we had overclocked all the cards, the gains on the reference card were more closely grouped at a gain of between 7 and 12%.