That's a 300W card before OC'ing. The PSU has a pair of 20 amp +12V rails rated at 480W. Along with the 77W CPU (before OC'ing), it is getting to the point there isn't much headroom left with the rest of the system's +12V loads. And at 80% efficiency, you are probably getting close to the margin. If you OC at all, I'd say grab a new PSU. The positive aspect, is that the Seasonic is a well made PSU. It probably wouldn't destroy anything if it became overloaded. It would just cause shut downs or reboots.