George Mulligan said:
The Gigabyte won't work, as 3rd PCIe slot would be x4. That Fatal1ty board would work for you. I'm a fan of ASUS for their quality and BIOS, but that's a Z87 board. Their Z97 board, "Hero", would have the same PCIe slot limitation as the Gigabyte board.
Have you considered 2 GTX980 instead of 3 GTX 970?
The problem is I already own a GTX 970.