Though it pains me to say it, Batman Arkham Knight is still an unplayable mess of a game. On PC we now have the latest Batman Arkham Knight patch and while it has increased frame-rates it has not stabilised them.
Batman Arkham Knight is not stable above 30fps – constantly wandering around by anything up to 20fps in some scenes.
At this stage I think the problem won’t be solved by optimisation. The engine is bottle necking constantly on the AI and with the huge LOD and large view distance it’s a recipe for bottle necking.
Basically this game was built for consoles running at 30fps and as soon as you try to do that on a PC at 60fps it falls apart and no amount of patching is going to make it rock solid and stable.