Here are the official power requirements based on your graphics card:
500 Watt or greater power supply with two 75W 6-pin PCI Express® power connectors recommended (600 Watt and four 6-pin connectors for ATI CrossFireX™ technology in dual mode)
This applies to the whole system not just the card.
As you can see you should be fine on a 650W unit and you have some headroom to spare. This will be handy with your overclock etc. You could probably get away with crossfiring on that unit. The link that you posted doesn't take me to a product...it says product not found but at face value and judging that it is an Antec unit, I would say it should be of good build quality and reliability.
Sorry, Link should be fixed now, thanks for your reply