Umm... I'm pretty sure the third slot will be for physics. The chipset supports 48 PCIe lanes, so why not make all three full x16? It's not like anyone EVER uses the 2x, 4x, or 8x (unless physically 16x)... EVER!
http://www.hkepc.com/bbs/itnews.php?tid=608109
Yeah, I'm gonna be getting this when Conroe comes out. But don't get crazy; that's just the reference board. The RD580 reference board was uglier. I hope ASUS makes the flagship RD600 have this layout
16x PCIe
PCI
15x PCIe
PCI
16x PCIe
PCI
PCI
But the latest boards show that ASUS doens't seem to like the top slot and they hate PCI slots!
A GPU for physics makes so much more sense economically. Instead of buying a card solely for physics, you have one that can aid in Crossfire in non-physics games and be used in physics games. Or when you upgrade your GPU, you can use your old one for physics! This will also help sell the lower-end X1Ks. All will be revealed this week!