I have 2 HD 6870 video cards . My driver version is crimson 16.2.1 and crossfire enabled. Some games are play good in crossfire mode but Americas army proving grounds , Insurgency, Guild wars 2 not run in crossfire enabled mode.
Those games do not have a native CrossFire profile. You can try adding those applications to Radeon Settings and configuring CrossFire to use a custom AMD CrossFire profile. More information available here.