Overclocking

To find the maximum overclock of our card we used a combination of GPUTool and our benchmarking suite.
The overclocks listed here 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.



The overclocks of our card are 955 MHz core (6% overclock) and 1385 MHz Memory (15% overclock). In my opinion this is good overclocking potential, even though I would have expected more from the HD 5870 Lightning. Also you have to take into consideration that the card is already overclocked out of the box. AMD's reference comes at 850 MHz only.

After I removed the cooler to take the photos, I wanted to go back to some more overclocking using additional voltage. I was shocked to see my temperatures up by ~25°C. After reassembling the cooler several times, and getting largely the same result, I took a closer look (added a sheet of paper to better illustrate the problem).



It seems that the mounting system of the cooler is not designed properly to apply enough pressure between GPU and heatsink. In the factory, a large chunk of thermal paste is applied, probably with some extra pressure, that hardens out and leaves good contact. With my own thermal paste I used a thin layer, probably too thin. Using more paste resulted in bad temperatures too, because the layer is too thick. Another sign that the contact is too weak is that you can rock the cooler back and forth by applying pressure to different sides of the cooler, which affects contact.

My solution was to add an additional washer between mounting springs and the card, so that the pressure increases. It took a few tries to get it right, but then I was seeing good temperatures again.

At the stock voltage I now got 965 MHz @ 1.165V. Bumping the voltage showed substantial improvements: 990 MHz @ 1.25V, 1025 MHz @ 1.35V, 1040 MHz @ 1.40V, 1045 MHz @ 1.45V, 1065 MHz @ 1.50V. Beyond that the card simply got too hot for any proper testing, I am sure higher clocks could be achieved with better cooling.

Hipro at XtremeSystems reports 1100/1377 MHz (core/memory) "on air with its default heatsink" and 1420/1420 MHz on LN2 at 1.430V.

Overclocked Performance

Using these clock frequencies (955/1385) we ran a quick test of Call of Duty 4 to evaluate the gains from overclocking.


The actual 3D performance gained from overclocking is 7.2%.

Temperatures

As I mentioned on the fan noise page, the idle temperature is too low given the excessive amount of fan noise from the card. Load temperatures seem reasonable, especially considering that a lot of people will increase the GPU voltage via Afterburner and try massively overclocking their card.

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 major performance scenarios and the GPU voltage that we measured. We measure on the pins of a coil or capacitor near the GPU voltage regulator.


AMD includes their own overclocking utility with Catalyst Control Center. While easy to use, it also limits the maximum overclock to a predefined limit in the BIOS. This limit may vary from vendor to vendor or product to product. Following are the upwards limits for overclocking CCC gives you.