do you have a multi-monitor setup? are the games' performance not satisfactory using all those monitors? does your motherboard have 2 PCIe 2.0/3.0 x16 running at 16x/16x, or 8x/8x? are you willing to risk the chance of microstuttering? if all the answers is yes, then by all means....
as for power, we're gonna need to know your PC spec first, though i reckon you don't need more than 650W unless you OC like a mad man