2D Temperature, Noise, Power Consumption
As long as you run the Radeon HD 5870 at its default clock speeds, you’ll see low power consumption. The GPU runs at 157 MHz in 2D mode and the video memory is throttled to only 300 MHz. As a result, our test system requires 152 W at idle, and that includes the overclocked 4 GHz Core i5-750 processor.
Overclocking is admittedly an issue with regard to power consumption. As soon as you increase the default GPU speed, which is 850 MHz on the reference board and 900 MHz on MSI’s R5870 Lightning, the 2D GPU clock speed moves up to 400 MHz. The main memory even runs at full speed. As a result, power, noise, and temperature increase quite a bit.
Using the preset clock speeds the R5870 Lightning cooler helps the card to run at 6°C less than the reference model. Once you overclock, 2D temperatures increase quickly. The overclocked reference board reaches 62°C in 2D at idle, which is only a bit less than what the MSI R5870 Lightning reaches at peak workload. In both cases, you’ll see temperature increases of 30 percent in 2D mode. Meanwhile, you have to switch to a 3D application to get any benefit from the overclocked settings.
The 38 dB(A) noise level is relatively low, though the 36 dB(A) default is quiet enough to make it almost impossible to hear the graphics card over power supply fans, hard drives, or processor coolers. In other words, you can literally hear the difference between factory speeds and overclocking.
As expected, power consumption goes through the roof when the cards run faster than their factory default. The R5870 Lightning requires 9 W more power at idle in 2D mode compared to the reference card. When overclocked, the Lightning consumes as much as 58 W more than the reference card's default. Keep in mind that the results were all measured in 2D, at idle. The high power consumption while overclocked is a result of the fact that idle clock speeds don’t drop to the lowest possible value once you overclock.
As mentioned in the introduction, you’d have to get a factory-overclocked retail card to avoid this. Or, you can create multiple overclocking profiles using your overclocking tool. Use the default clock speed for 2D operation and the overclocked settings for 3D gaming action.