I am not familiar with that particular PSU. Antec does make good PSUs, but for 6850s in crossfire, I'd rather have a little more headroom on the power supply, as they are most efficient when run at about 50% capacity. I'd look for a Corsair, Seasonic, or Antec Earthwatts in the 650 to 750 watt range.
As far as gaming goes, there are very few games that take advantage of more than two cores. the 555 is rated as one of the best dual core AMD chips. That being said, I would suggest the Phenom II X3 black edition 720 or 740. With the MoBo I listed, there is the possibility of unlocking an extra core, giving you an X4 for the price of an X3.