If you want to evolve, you should also add the H110 pro btc from Asrock with 13 pci slots. I'm using this one and price has seriously gone down which makes it more attractive than 6 months ago.
thats a thought. My goal was going to be around 6 cards per rig. I wanted to space the cards out for heat issues. if I tried to squeeze more cards in I figured they would get to hot being so close together