I strongly recommend this Pro series PSU
im running a 4870, an oced X2 @ 1.57V and a couple of HDD, DVDRW and many other stuffs on a Pro 550.
Extremeoutervision's PSU calculator says it ll need a 540W PSU and this PSU is able to meet the need unlike CM EP series which cud deliver about 50W less than rated wattage.
ive completed 3DM 06 bench and OCCT tests successfully on it. Actually on searchin, i got results that its HEC OEM, which are quiet good.