@rinnowaru: Wait what? how could a 970 preform that badly? On what processor?
I saw some explanation that the biggest issue is how it handles anti-aliasing. There are several different ways to do anti-aliasing (SSAA, MSAA, FXAA, etc). Usually when you turn on AA in a game, it defaults to whichever one of those is the fastest method (and then often gives you the option to dial it up to a slower, better looking method). What I've read is that Nier defaults to the best looking (but slowest) method of AA.
So instead of the AA options being on a scale from none->low->medium->high->higher->highest, the AA options are none->higher->highest. In other words, turning off AA altogether makes the game run MUCH more smoothly than having it active on it's "lowest" setting.
I could be completely wrong about all that though.