A Steam Community Group Announcement from Rocksteady Games addresses performance in Batman: Arkham Knight, or more accurately the poor performance of the PC edition of the just-released superhero sequel that has drawn fire from unhappy customers (more than two-thirds of the game's Steam reviews are negative). They remind those who purchased the game through Steam how to get a refund as they say they are looking into how to improve things on their end, and warn against trusting the recommendations of NVIDIA's GeForce Experience or AMD's Gaming Evolved Optimization tools. In the meantime offer another update to the game's system requirements to retroactively acknowledge the issues and some setting recommendations to smooth things out. The settings all note the 30 fps cap, and they warn against the workaround that involves ini editing. Here's word:

The Recommended Spec is intended to deliver an experience on par with the current generation of gaming platforms.

For an optimal experience, users with recommended spec hardware should not set their resolution higher than 1080p.

By default, the game may set Shadow Quality and Level of Detail to High on Recommended Spec hardware. Users should revert these to Normal.

With these settings on Rec Spec AMD GPUs, users can expect some minor texture pops, occasional loading symbols during fast-paced scenarios, and some hitches & stuttering when gliding or driving the Batmobile. To help alleviate this, AMD users using Rec Spec GPU’s should turn Texture Resolution, Shadow Quality, and Level of Detail to Low. We continue to work closely with AMD to resolve these issues as soon as possible; make sure you have the most current drivers and check back here for updates on when the next driver version is available.

Additional Recommendations
We do not recommend that users change anything in the game’s .ini files as this will potentially negatively impact performance, including frame rate, and stability.

At this time we do not recommend using NVIDIA’s GeForce Experience or AMD’s Gaming Evolved Optimization tools.

We’re currently working on improving streaming performance from mechanical hard drives (HDD). Addressing this is one of our top short-term priorities.

For users that have an SSD available, we’ve noted increased streaming performance when the game is installed to that type of drive.