So AMD has released new GPUs. Of note is that Crossfire is now PCIe 3.0 based, that is no special bus required. Of course Apple could plumb that bus in addition to PCIe, but now I think it's moot. How they managed dual GPUs has been an open question, and with those small daughter boards it wasn't clear what they would do. My prediction then is the new "FirePro" cards will really be Hawaii RX GPUs with embedded crossfire enabled. This would imply that under Windows BootCamp gaming it would work and be formidable.