Overclocking

The overclocks listed in this section were achieved with the default fan and voltage settings as defined in the VGA BIOS. Please note that every single sample overclocks differently, that's why our results here can only serve as a guideline for what you can expect from your card.



Maximum stable clocks of our card are 910 MHz core (7% overclock) and 1500 MHz Memory (15% overclock).

Overclocking potential is decent, substantially higher than the reference design and about in-line with what we have seen on the PowerColor PCS++ HD 6950.

Overclocked Performance

Using these clock frequencies we ran a quick test of Call of Duty 4 to evaluate the gains from overclocking.


Actual 3D performance gained from overclocking is 8.3%.

Temperatures

Temperatures look fine. Again, I tested with both fan configurations: both Vertex fans all the way in and all the way extended. It looks like there is no measurable difference between both settings.

Voltage Tuning

It has been a long known fact that overclocking headroom increases as soon as you increase the operating voltage. Until recently, software voltage control on VGA cards has been the exception and most users were not willing to risk their warranty by performing a soldering voltmod. Nowadays almost all current graphics cards have voltage control in order to achieve low power consumption by lowering voltage when in idle or slightly loaded.
In this section we will increase the GPU operating voltage step by step and record the maximum clock speed possible. Voltage is listed as the value that the voltage regulator reports via software, not actual measured voltage. The card was installed in-case, with fan settings at default, memory will not be overclocked either. If a card has thermal throttling we will reduce the operating frequency to keep performance as high as possible for a given voltage. Please note that the fan profile will have an effect on observed temperatures: if the card gets hotter the fan will ramp up to reduce temperatures or keep them from rising fast.

The following graph shows the overclocking potential we saw on our sample. GPU clock is represented by the blue line, which uses the vertical clock scale on the left. The scale starts at the default clock to give a feel for the overclocking potential over the base clock. Temperature is plotted in red using the °C scale on the right side of the graph. An additional graph shows full system power draw in orange, measured at the wall socket when running at the given voltage, clock & temperature.



PowerColor's HD 6950 Vortex II gains very nicely up to 1000 MHz at 1.3 V. Beyond that setting the card felt very unstable and showed rendering errors and crashes - even at reduced clocks.

Modding to HD 6970

Last year it was discovered that the HD 6950 can be modded to HD 6970 by BIOS flash.
I tried the mod by saving the BIOS, loading it in RBE, clicking the "unlock shaders" option and flashing the BIOS back to the card.



The mod worked well, and all shaders are unlocked.

Clock Profiles

Modern graphics cards have several clock profiles that are selected to balance power draw and performance requirements.
The following table lists the clock settings for important performance scenarios and the GPU voltage that we measured. We measure on the pins of a coil or capacitor near the GPU voltage regulator.