I know I can crossfire a 4850 & 4870 as even though the 4870 is reduced together they are betther than a 4870. What I'm wondering is as the 4850 is a legit Mac Pro GPU will it work in my PC and if not can I put my 4870 in the Mac!?
I wouldnt see why not. The best thing to do would be to put mac pro GPU into the PC and see what happens. I have never actualy heard of someone doing this so my guess is as good as yours im affraid. It should work unless the pci-e connector is different which i doubt it. Although Apple is very proprietary when it comes to graphics cards wich leaved me thinking it may not work. If the pci-e is the same as PC it could work however you would need to flash the cards bios to make it read in PC language not Mac. So it would be a hole lot of mucking around. I would just suggest to save up and go Xfire with your PC, as mac GPU's cost a lot more. Hope i helped.