Your better off disabling crossfire until AMD actually release drivers that implement it properly (and no, 13.8b2 do not do a good job despite the driver notes including FFXIV).

As it stands, the scaling is inconsistent at best (dual 7870's here) and the fps frequently raises and drops for no discernible reason. Its also very well documented on these and other forums that each card will only be running 50-60% in crossfire/SLI due to the poor driver support right now (slightly better with FEAR profile fix) - this includes people running older cards and those running dual gtx 780s in SLI for example.

I'm assuming that your running in full screen mode... (crossfire, by design/limitation not working at all in windowed or full screen windowed mode etc etc).