Thankfully there is a way to unlock the 30 frames per second cap, which should have you maxing your PC's capabilities in no time.
To remove the cap you need to edit the BmSystemSettings.ini found in the folder: STEAM_INSTALL_FOLDER\Batman Arkham Knight\BmGame\Config
Open the BmSystemSettings.ini file in a text editor and search for "Max_FPS=30". Once you've found this entry simply change it to read "Max_FPS=9999". Save and exit.
When you next load up the game you'll have have an unlocked frame rate.