Overclocking the HIS Radeon HD5870
To overclock the HIS Radeon HD5870 all I had to do was unlock the Catalyst Control Center which gives me access to overdrive screen. The ATI overdrive allows you to manually set the Core clock, memory clock, and the fan speed. The Catalyst Control Center is bundled with the driver from ATI.
I was able to push the Core clock to 900MHz from 850MHz this put the HIS Radeon HD5870 at the maximum allowed by ATI's Overdrive utility. The memory was able to be pushed from 1200 MHz up to 1300 MHz, which again is the maximum allowed by ATI's Overdrive. To check stability I ran FurMark 1.70 for a minimum of 15 minutes followed by 3dMark Vantage.
Starting with a combined score of 18379.
Being limited by ATI's Overdrive utility we were still able to achieve a boost in 3dMark Vantage, though not a record score it is still a great score for a single card. Although I have only used ATI's overdrive in previous reviews I did try to use both ATItool and Riva Tuner to overclock the HIS Radeon HD5870 though neither of those utilities support the 5800 series cards yet.
Benchmark Results: Having the ability to max out ATI's Overdrive leaves me to believe that the HIS Radeon HD5870 has alot more overclocking headroom.