"I get better frame rate with the 12.7s but any crossfire profile I use renders
bad flickering. "
I had the same issue - I also tried the Lost Planet DX9 and DX11 profiles. Try playing with the Vsync settings - turned off in CLOD and "wait for vertical refresh" in CCC. I am still experimenting myself
Could be your linked cards are different?? I have two identical cards linked with Crossfire.