I noticed that EVGA GeForce GTX Titan has two PCI-e power connectors: 8 pins and 6 pins. Can we connect only one of them or must we connect both power connectors? If the answer is the former, what is the difference between 6 pins and 8 pins (8 pins can support more powerful computation, I guess?) If the answer is the latter, does CORSAIR CX750M PSU have 8-pin PCI-e power connector? If not, what CORSAIR PSU model has both 8-pin and 6-pin PCI-e power connectors output? Thank you.