I would go at least 600W. You will be shure not to get over the advised limit of 80% load and it would be more than enough to power that.
Just make shure it is a quality psu. And it will even last when you decide to upgrade to other components.
And if you go something like 700W (although a bit overpowered) the psu will run allways cool with little to no need to turn on the fan wich mean it will also be more silent.