I have two VTX3D 7970 cards in my machine. They are at the stock clocks 925 / 1375 @ 1174mv. I have tried to overclock but the highest I could get the core is 1055 before I got errors immediately in OCCT (or the PC just hangs). Increasing the core voltage doesn't seem to make any difference, in fact if anything it made it worse. I tried the voltage at 1.300 (not intended for 24/7 use, I just wanted to know the limits of my cards) and OCCT crashed even with the cores at 958. My GPU memory on the other hand seems to work fine, it reaches the max allowed in afterburner (1575) with seemingly no problems. - Is it harder to overclock these because I am running crossfire? - Should I have overdrive set to 0% power limit when increasing the voltage manually? - My 2600k is overclocked to 4.8Ghz (Asrock Extreme7 Gen3) are there any BIOS settings that might be affecting my graphics card OC? Please advise!