I would just snag some PCI-E power splitters. http://www.ebay.com/itm/290778077889?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649 Running gfx cards off a molex is bad. It's too much load on that single 12v. Thats why PCI-E has 3 12v and 3-5 grounds. I own about 26 of them in my basement mining rigs, never had a problem. Last time I used molex for my gfx cards, I melted the wire and the modular connection at the power supply and killed the port, and that was with only 2 radeon 5850.
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