The 5850 uses a maximum of 170 watts at full load. Your entire system might use 300 watts under a full load. Draw your own conclusions.
Here is a review of the 600 watt version of your chosen PSU. It gets a pretty good rating: Coolermaster Silent Pro M600 Review
The Arctic Cooling heatsink is pretty good, but if I was going to overclock I would probably get the Coolermaster Hyper 212 in the same price range. If I was not going to overclock, I would just use the stock Intel cooler unless you have an aversion to its high pitched whine under load. Most people aren't bothered by it.