Psst. AMD fans. Don't tell "Team Green" but Linus decided to take four R9 290X graphics cards and configure them in Quad Crossfire formation. They did not seem to have too much difficulty setting it up, although they did have trouble with throttling and setting up Crossfire profiles. When they finally were able to test it, they got a 3D Mark Fire Strike Extreme score of 14979.
Psst. NVIDIA fans. Don't tell "Team Red" but Linus decided to take four GeForce Titan Black graphics cards and configure them in Quad SLI formation. He had a bit of a difficult time setting up the machine at first, requiring a reshuffle of the cards (how would reordering PCIe slots for identical cards do anything?) and a few driver crashes, but it worked. Eventually, they got a 3D Mark Fire Strike Extreme score of around 13,300 (give or take a couple hundred).