Don't think this was posted yet, originally posted at: ~***Offical ATI 1000MHz Core Club***~ (Updated, sorry guys) - Overclock.net - Overclocking.net
I attemped this and asked advice from some people and didn't really get a straight answer as to steps. So I indulged myself to figure it out.
I also wanted to inform those of you having issues enabling the "unofficial Overclocking" feature in the MSIafterburner Program for convenience of NOT having to use Both the AMD GPU Tool (to change the frequency) AND MSI Afterburner (Just for the voltage). And to try this Before Flashing the BIOS like some are attempting, when the issue really may only be taking the right steps to change the .cfg file and saving it properly...
Here are instructions on how to do so. Make sure that you follow step #4. Otherwise it won't work!
1.) Open the MSIAfterburner.cfg with Notepad
2.) Change the "enable unofficial overclocking" Value of 0 to 1.
3.) Select "File" and select "Save as".
4.) When the save window pops up select "All Files" in the "Save as type" box and save!
It wil ask you to confirm the "Overwrite of the file" Select "yes".
You are done and should be able to Use ONLY MSI Afterburner to overclock your ATI Series Card past the max CCC Frequency!
This allows you to get past the 900MHz core block (and memory speed block) for certain brands of the HD5870 GPU.