Windows 10 64 bit + 2x Radeon 7770 + Crossfire bridge + Crimson Edition 15.12 = Crossfire doesn't work
So 1x7770 10% faster in games and in 3dmark 2015 then 2x7770. Crossfire checkdox is switched on at driver settings!
How it could be? Slave card is worming up only with 3dmark 2015 but the results are lower of the same like with 1x7770, but with different games it is cold like ice!
Install an OSD like RTSS and HWiNFO so you can see GPU usage in fullscreen games. You might want to re seat your GPUs and the bridge. Use the GPUz link test to check both cards are using the full PCIe link speed.