Ya you'd be lucky to hit 8.5GH/s. I'd say you're prolly closer to 8GH/s, but it depends on how far you can OC each card.
Most people assume an average of ~100W for your motherboard, CPU, and everything that's not the GPUs.
Those GPUs will each use about 250W.
Your PSU is an 80Plus Gold, so that's nice. However, it's not a single rail PSU. It's got 6 rails, which is bad for mining. I'd suggest
THIS one. Each rig will pull ~ 1100W, and that PSU can handle that no problem.
Totaly, you're looking at ~3.3kW.