I have recently acquired a XFX Radeon HD 6870 Double Fan. I have been overclocking it to around 980~ for core clock and 1150 for Mem clock. I've tried to go higher, but to much disappointment, the card would get artifacts. So I left it at the settings I specified above. I have recently been taught that raising the voltage would make the overclocking headroom higher. But in MSI afterburner, all the Voltage settings are locked. i have tried to unlock them in the settings, but after ticking the settings "Enable voltage control" and "enable voltage monitoring" I have not been able to move the sliders, as they were grayed out. Is this because my card is not reference design? Is it because my card's bios isn't compatible?