which mainboard has much pcie ?
it seems GA-X58A-UD9 has 7 pcie(*16) ,which MB has more than 7?
ATI driver can only support 8 card in 1 system at most ?

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MSI Big Bang series supports 8 PCI-E v2 x16:

8 x PCI-E 16x

7 x PCI-E 16x

The slot widths are only 1 space and each card will use 2. As AMD drivers only support up to 8 GPUs, I'd wait for the AMD HD 7990 as you'll only need 4 cards as each will have 2 GPUs. The other things you'll need to consider is power as 1 PSU will not run that many cards. If you did want more single GPU cards, you would have to use a custom case design and use PCI-E extenders.
gigabyte ud7 6x pci but much much cheaper then the others here also you dont need a expensive slow inten cpu , you can run it with a nice 8150 amd power cpu...