This was posted by someone else:
Download MSI Afterburner/MSI Kombuster (Kombuster comes with afterburner)
Install them both, go in to the settings on Afterburner and select enable voltage monitoring/changing etc.
Then slowly start to increase your core clock by 5-10MHz at a time while running MSI Kombuster.
Once it starts getting unstable bump up the voltage by 25 - 50mv at a time.
I should imagine you would be able to achieve up to/around 850/900MHz. They're very good overclockers, much like it's little brother.
end of post.
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