My silverstone 1200w psu came packages with several pcie cables with both a 6/8 + a 6 pin which split off after the 8 pin. I am currently in the process of replacing my old sli 580s and was wondering if I'd be safe using just one of these cables to power my new gpu (gtx780), I have noticed that the individual cables that come directly from the psu are noticeably thicker than the ones which split off to the 6 pin. Also I would mention that the psu has a single +12v rail which is rated for 100amps.
I hope what I'm trying to ask makes sense as I'm posting this from my phone while at work.
I would add that the psu in question is a silverstone strider gold 1200w