A post from the developer at B3D.
We reach double frame rate compared to the "graphically demanding titles" such as Infamous Second Son, Killzone (SP) and Assassin's Creed.
720p @ 60 fps is slightly more demaning than 1080p at 30 fps
900p @ 60 fps is almost 50% more demaning than 1080p at 30 fps
1080p @ 60 fps is twice as demanding than 1080p at 30 fps
We chose frame rate (= gameplay). Other developers had other priorities. For our game 60 fps is the best choice.
There aren't many 60 fps locked games on next gen consoles. We are locked 60 fps all the time, not fluctuating 30-50 fps like most of the other "60 fps" games.