First things first: the performance gains you get when you spend an extra $100 on an overclocked card are quite limited, which is due to the relatively small clock speed boost of 850 to 900 MHz that equals only 6%. In our gaming benchmarks this translated into an even smaller 1.5% gain (hardly worth a 25% increase in cost).
On the reference card, we reached the same 900 MHz, but we also accelerated the video memory from 1,200 to 1,300 MHz, which results in a more significant performance benefit of 4.5%. Last but not least, we also overclocked MSI’s R5870 Lightning to 925 MHz on the GPU and 1,315 MHz on the GDDR5 video memory, which resulted in a performance advantage of 5.4% when compared to reference clock speeds. That's an extra .9% gain overall.
As you can imagine, the MSI R5870 Lightning doesn’t hit physical limits at these speeds. You can use the Afterburner tool to tweak voltages in an effort to reach higher overclocking speeds. Once you enable voltage control in the settings window, you will be able to modify an additional slider in Afterburner. The default GPU voltage setting for MSI’s R5870 Lightning card is 1.129 V. We decided to finalize this article without voltage increases, because the potential performance increase is disproportional to the strain the card has to endure. We needed more than 1.2 V to make sure 950 MHz would work reliably, and this came at the cost of 73°C GPU temperature. All you would be getting is a mere 1% performance boost, which is not quite exciting. The memory could hardly be overclocked any further than 1,315 MHz. The TwinFrozr II fan will also be running at increased speeds, generating more noise. Our recommendation is to use the voltage control for ensuring stability at slight overclocks instead of going for maximum clock speeds.
The performance diagram shows the frame rates during the 13 minutes benchmark duration. The black area shows the performance of the reference card. The green peaks represent the additional performance of the overclocked retail card. You can see that there is additional performance at low as well as at high frame rates. We used a 1920x1200 resolution with 8x anti aliasing.