One interesting caveat here is that AMD is limiting CrossFire support two dual-GPU configurations. Just like NVIDIA, the red team is no longer officially supporting CrossFire configurations with three or more GPUs.
AMD send out a low-res chart that reveals the CrossFire GPU scaling performance. Overall, the company promises a performance boost of about 80 percent versus a single card, give or take a couple of percentage points.
It's unknown when we can expect these drivers, it will probably be Friday or sometime next week.

Source: TechPowerUp