I have a cooler master silent pro gold 1200w psu and a single pcie cable has a 8 pin connector and a 6 pin connector should I just use one cable to power a hd 5970 or would I need to use one cable to power the 6 pin port and another cable to power the 8 pin port On the 5970
Sometimes, different pci-e connectors will be hooked up internally to different 12V rails.
Your PSU seems to have one large 12v rail.
So it would seem that it does not matter and you can use both 6+8 pin connectors stemming off that one cable.
Part of me, wants to wonder if the gauge of the wire can safely pass along all the current that those two connectors are spec'd for. I'm guessing they are.
Other lesser psu's it might not be ok, to make your own splitter and force a 6+8 pin off a single cable.