Enabling Crossfire Only Swaps Cards

One of those cards in gpu-z has the shader count of a 280x, not a 270. They also are both reporting as 2gb cards, not 4gb cards. Ive seen afterburner and gpu-z report double memory usage in crossfire though, might just be the way the driver reports it. The 270 is also the exact same card as the 270x at a lower clockspeed, and they are absolutely crossfire compatible.

you might have a wrong bios on one card, or corrupted drivers. And you need to make sure you are running the game in full screen, full screen windowed doesn't count either. Crossfire only works in windowed mode on mantle enabled games.