Stock clocks on the HD 5870 are 850 MHz core and 1200 MHz on the memory and are locked to a mild OC of 900 MHz / 1300 MHz using ATI CCC or MSI AfterBurner. Fast enough, but not fast enough for real overclocking!
However thanks to ASUS and MSI, you can flash your reference 5870 to an unlocked BIOS.
Caution: I am not responsible for your result, proceed at your own risk. If you don’t have experience flashing GPUs and have a spare card, you can use it to flash back to your original BIOS.
We will use the Asus unlocked BIOS (which ships with the Asus Card) to increase our OC limits to 1200 MHz core and 1400 MHz memory. If you have high-end GPU cooling, then you can try the MSI unlocked BIOS which increases the core and memory to a ridiculous 1800/2600.
I always use a USB stick with a bootable DOS image on it to flash my Motherboard, GPUs, SSDs, etc – use this program HERE to create one.
First, make a backup of your original BIOS using GPU-Z.
Download the Asus unlocked BIOS HERE.
Download the latest ATIflash tool HERE.
I created a directory on my flash drive called ATI. In it I put Atiflash, my original BIOS, and my unlocked BIOS. I always rename my BIOS to something short so I can read them in DOS as it doesn’t like long file names. For example I renamed the Asus BIOS to unasus.bin
Once you have assembled all the necessary files, reboot your machine to the DOS prompt and navigate to the appropriate directory (in my case ATI). You can do this by entering “CD ATI” once you’ve booted off the flash drive.
Then the command is atiflash -f -p 0 unasus.bin (or whatever you named your BIOS).
-p Write BIOS to image to all appropriate adapters
-f Force flashing regardless of security checking BIOS file info check OR boot-up card
0 is the number of the card in your system.
Reboot to Windows and most of the time you will have to reinstall the ATI drivers as it now sees a whole new card.
Now check out CCC and you will see you can now advance to 1200/1400. I also use MSI’s afterburner as it allows you to increase your voltages up to 1.35v as well. Like any other OC, the key is go slow, take your time, and always check your temps.
I managed a nice 3DMark06 run with a 1050/1250 OC and 1.30 volts. This was good for a top 20 score on HWbot.org.