I have a HIS Radeon iCooler V 5870, and lately I've been trying to overclock it. I downloaded MSI Afterburner, ramped it up to 900MHz (the most the slider would go up to) and played a while, and all seems well. I'm interested in going a little further, but the slider only goes up to 900MHz. Meanwhile, I hear about people clocking their 5870s much higher than just 900MHz. I can only set the slider to 900MHz, how do I break this limit?