At the AMD event here in Sydney, Australia AMD were powering a 5K monitor running Dragon Age: Inquisition with a single Radeon R9 Fury X card. The heat output from the back of the included radiator was surprisingly cool, and not even warm.
Given that it's rendering a huge 5120x2880, a single Radeon R9 Fury X is a powerhouse of a video card.
It was liquid smooth to my eyes, with the graphics being set to 'Medium' at 5K. It felt like 60FPS+, which was absolutely astounding to see in person... 5120x2880 on Dragon Age: Inquisition from a single video card. Yes, please AMD.