One great video cards will be better than two lesser ones in someways, particularly on that MoBo as the PCIe connections for them will be running at half speed. And you will only have the memory of one card. Also consider that some games do not play well with dual GPUs. One card would be cheaper and by the time the extra power is worth having you could upgrade to a new GPU that will likely be more powerful than both of them together (and by then 1 GB of video memory may no longer cut it).
I would also recommend the LIAN LI Lancool PC-K63 Black Steel ATX Mid Tower Computer Case. They are fairly equal, but this one is about $50 less.
Might be worth getting a small SSD to install the OS on, such as the Crucial M4 CT064M4SSD2. Also two Wester Digital Caviar Black 7200 RPM 500GB in Raid (I think 0 is striping) would be better as smaller drives tend to be more reliable.
