Found the little buggers: for a mere €1,086.99 a piece they trade owner (under the veil of [BOLD]Opteron 6174[/BOLD]). The Mobo, an Asus KGPE-D16, goes for €448.99. Supports up to 256GB Registered ECC or 64Gb Unbuffered ECC/non-ECC DDR3 memory at speeds of 800, 1066 and 1333MHz. Quad-Crossfire possible: four PCI Express 2.0 x16 slots.
Given unlimited money, two 6174s on this mobo give you 24 cores and together with 4 HD5970s and 256 Gb RAM you should be able to crunch your way to the #1 spot.