= $1337 <--- that alone is a great reason to buy it lol + you get free mafia 2 game.
Need an OS? Add $100 for windows 7.
I'd recommend the p55 setup instead of the x58 because you wont see any difference in fps between the 2 setups, and its cheaper. I also recommend 1x 480 instead of 2x 460 even though they perform slightly better in some cases. The reason for this is that your already getting a 1000w psu, and you'll have room to sli in the future for some serious kick*ss.
With OC and stuff :
2 GTX480s will need I would say about 850-1000W.
HD5850s need less power, 2 of them will need about 650-750W.
But GTX480 is indeed more powerful than HD5850.
I always choose the best for the PSU because a defect PSU can damage your whole rig. I would choose Corsair, Seasonic, Antec, Enermax, Tagan, SIlverstone, or PPC. To reduce the price of the PSU, choose the none modular one.