Wasting no time, we started ratcheting up both the GPU and memory speed. At default voltage, we were able to reach a maximum stable overclock of 935MHz GPU and 1280MHz Memory. This is a gain of 85MHz and 80MHz respectively. We were able to get the card to run at 950MHz but would lock up midway through the second 3D Mark Vantage test. With a little more voltage 950-1000MHz should not be a problem on the Radeon HD 5870.
Article Title: AMD Radeon HD 5870 Video Card Overclocking
Article URL: http://www.legitreviews.com/article/1090/1/