The evidence is in black and white in the following benchmarks. The Cinebench result shows just how far ahead of the Gigabyte 970A-UD3 the two Asus 990 boards are in getting the most out of the CPU. The power draw is also rather interesting, with the high-end RoG board the most eco-friendly.

X264 HD v4.0: Frames per second (bigger is better)
Asus M5A99X EVO: 32.7fps
Gigabyte 970A-UD3: 32.5fps
Asus ROG Crosshair V: 32.9fps

Cinebench R11.5
Asus M5A99X EVO: 5.86pts
Gigabyte 970A-UD3: 5.78pts
Asus ROG Crosshair V: 5.86pts

PCMark Vantage
Asus M5A99X EVO: 9252
Gigabyte 970A-UD3: 7118
Asus ROG Crosshair V: 8511

Stalker: Call of Pripyat (1280 x 1024, low, DX11, Day)
Asus M5A99X EVO: 165.79fps
Gigabyte 970A-UD3: 157fps
Asus ROG Crosshair V: 163.6fps

Power use (Peak): Watts (lower is better)
Asus M5A99X EVO: 305W
Gigabyte 970A-UD3: 318.9W
Asus ROG Crosshair V: 299W