Oh if you do go the Radeon 7770/6850 route I found this powersupply to work really well for me.
I built two PCs with a 600W Diablotek
http://www.amazon.com/Diablotek-Series-600-Watt-Supply-PSDA600/dp/B003UWNL2O/ref=sr_1_2?ie=UTF8&qid=1344277897&sr=8-2&keywords=diablotek
One PC with it I've had for 4 years
Phenom 9600 Quad-Core BE OC'd to 2.5GHZ
Radeon 4850
4GB 1066mhz kingston hyper-x memory with 5-5-5-15 memory times
3 hard drives - 250GB Seagate HD with 8mb cache, 750GB Samsung F1 with 16MB cache, 1TB Western Digital Blue with 32MB cache.
Dedicated Creative Sound card
Foxconn A76ML-K (DDR2 Version) Motherboard with max TDP of 95W
Running games games of just about every genre on a regular basis. Crysis/Warhead, Doom3/Quake 4/Wolfenstein (2009), Unreal 2-2.5 engine games, Unreal 3 engine games, World of warcraft, Starcraft 2, Two Worlds, Assassins Creed1+2/Prince of Persia, etc. The PSU is still holding strong.
I was impressed so much that I bought a second one for the build for a relative that is exact same except it had a similar performing Athlon II 450 3.2GHZ triple core processor. My cousin has had the system for about a year and a half now, and so far no complaints.
It may be labeled as a 600Watt PSU, but don't use it as a 600W PSU since it is a cheapo. Treat it like a 350-450 watt psu. For only 30$ you can't beat it.