use your first setup with 8 gpus, but not the hd6 crap, put some nice HD5850 on it, expinsive but powerfull, 2 good PSUs with 800-850W and it will be fine.
It will give you about 2,9Ghash
And btw, why have you choosen such expensive boards with full 16 physical lanes per pci-e slot? there are much cheaper boards with just 2 or 3 pci-e 16x slots and a few pci-e 1 slot.
Its better to go for the cheap ones, as you surly know, the amount of lanes doesnt matter per slot.
I'm not actually making these. The reason I picked the 8 pcie x16 because its the only board with 8 pcie slots. In order for the 6770 or the 5770 to compete you need to minimize the costs of all the other materials by loading a board up with as many as possible.
I was just trying to be creative so people would think out side the box.
Also if you want to post the set up your talking about with 2.9 ghash and get the megahash to dollar ratio then we might get the ball rolling.
