I will say I like the factory overclock because it allows the card to idle properly. With overdrive on ( or afterburner) it can not idle below 400/1200, with it off 157/300 and running basic windows and internet it stays there. it keeps it cool and i assume it saves power.... And it is stable @900/1200 on stock voltage, can move overdrive sliders to 1000/1300 but haven't tested it yet .
My card came with a molex to 6 pin adapter cable and a twin molex to 8 pin adapter cable.. in the box. So it must work, my psu is 750W