I'll have to look at this more in depth, as I run two 7970 GHz GPUs in Crossfire, and can directly rebut this:
with this: »As requested, Crysis 3 benchmarks
Where AMD has definite issues is with HD 7970s in CrossFire, and our Frame Rating testing is bringing that to light in a startling fashion. In half of our tested games, the pair of Radeon HD 7970s in CrossFire showed no appreciable measured or observed increase in performance compared to a single HD 7970. I cannot overstate that point more precisely: our results showed that in Battlefield 3, Crysis 3 and Sleeping Dogs, adding in another $400+ Radeon HD 7970 did nothing to improve your gaming experience, and in some cases made it worse by introducing frame time variances that lead to stutter.
Those who would give up Essential Liberty to purchase a little Temporary Safety, deserve neither Liberty nor Safety.