I just built two of these systems, so this may be helpful for you:
MSI 890FXA-GD70 with Sempron 140
CORSAIR 950TX P/S
HAF-X Case with 1 additional 200mm top fan, 1 additional 140mm inside
4 Saphire 5830 GPUs
1 7200 RPM HD

Overclocking the GPUs to 950MHz Core, 300MHz Memory results in 288Mhash/sec.

Power draw is 668 Watts while hashing, even with fans set at 100%.  At least according to the Kill-A-Watt.