The connector ITSELF is rated for 288 watts - but the WIRING to it out of most power supplies is commonly NOT rated more than perhaps 150-200.

 Splitting a 6-pin to a pair of 8-pins is A VERY VERY BAD IDEA.

 The connectors on the EVGA G2 1300 POWER SUPPLY aren't wired the same as PCI-E connections - I'm pretty sure they are using 4 pins each for +12v and ground, so those should be able to handle 350 watts or so - given that the PCI-E spec for an 8-pin connector limits it to 150 watts, you should be able to safely run an EVGA-type dual-cable from EACH of those connections on the power supply as long as you don't exceed it's total power capacity.


 The PCI-E spec is VERY VERY conservative on avoiding overload on the power connectors.
 Don't confuse THAT spec with what the connector ITSELF is actually rated at.