Batman: Arkham Knight launched with rather massive frame rate issues on PC, and while Rocksteady promised a fix, you can help yourself in the interim.
There is one main culprit for the problem, and that’s motion blur. It almost single handedly halves frame rate whenever it kicks in, and for some inexplicable reason, the developers decided (just again) not to let us turn it of in the options.
In order to kick the damn thing out of the picture, go to your Steam\steamapps\common\Batman Arkham Knight\BMGame\Config folder and locate the file BmSystemSettings.ini. Make a backup copy of it and rename it BmSystemSettings.bak, then open the original file.
For most users, touching the main motion blur settings (MotionBlur, MotionBlurPause and MotionBlurSkinning) causes the game to crash on startup, but you can try to change them respectively to MotionBlur=False, MotionBlurPause=False and MotionBlurSkinning=0 to see if the game still works. If it doesn’t (as it’s probable), change the values to their original and move on.
To solve the problem without risking crashes, set the following values:
This will kill off most of the motion blur, and restore your frame rate.
Of course, this begs two questions: how is it possible that whoever tested the PC version of the game didn’t notice the massive frame rate drops caused by motion blur on basically every configuration? It took me about 10 seconds to figure out that motion blur was the problem. Just looking at it and turning the camera around makes it absolutely obvious to the naked eye.
Secondly, how is it even considered acceptable by a developer, in this day and age, to launch a PC game without a proper configuration option to deactivate motion blur?