Would a Radeon 3870 Mac Edition be compatible with a PC purchased 3870x2 for crossfire under windows? I've heard that standard 3870s for PC (such as the Sapphire) are recognized in OS X and Windows when paired with a Mac Edition 3870. I can buy a 3870 Mac Edition for a good price, but am curious if I opted for an X2 on top of my single 3870 would give any significant improvements over two Mac Edition 3870s paired together? And more importantly, would it work? Also, is the Mac Pros (2007) PSU enough to power a 3870x2 and a 3870 at once? Thanks!