My 6950 toxic has this in the sapphire bios. It runs totally stable with 950/1350 clocks and all shaders unlocked. VDDC is 1.176 according to gpuz. So yes, you need 1.175v for 1536 shaders ( or 6970 settings). The amount of overclock depends on your card ofcourse, there will always be differences. But also yes, I would say 900/1400 should be easy since it's usually harder to oc the gpu compared to the mem. Beware of heat though. ps. those voltages are under load ofcourse, it idles at 0.900v. ps2. my card is made to run at those 6970 settings, albeit not guaranteed by sapphire, still it's quite able to run 880/1300 easily, leaving much headroom for more overclocking, this can be found in various reviews also. That's not something that applies to all 6950 cards, could be some can only do 850 or slightly higher for the gpu.