Build #3 would get you more credits/day just because of the additional GPU space. Or picking up another Big Bang Marshal and some of F$'s PCIe extension ribbons and the Cosmos II, though it prevents using a hex-core CPU.
Or the EVGA SR-X board. Dual Xeons that you can overclock with 7 PCIe slots.
I can only imagine the puddle of drool you must be sitting in right now