Probably it's one of the most important components, and very often they costs as much as a good video-card. Keeping a PSU on its limit can lower the stability of your system, give lower alimentation quality (hence lower frequencies you can reach in overclock, or higher stable volts), higher failure probability (stopping entirely your rig) and probably higher power usage, caused by a lower efficiency.

The card TDP is 150W, a good indicator of its power needs, and according to this link https://en.bitcoin.it/wiki/Mining_hardware_comparison I wouldn't go below a 1000 watt. Probably the best solution is a Quad-Sli (or quad-crossfire) certified PSU, also because they have enough 6pin connectors and you don't need too many adapters.

Do some research, very often the "overclock branded" PSUs are white-label from OEM makers (i.e. Fortron), and you pay more just for the service, not the product quality itself.