I usually don't pay much attention to framerate issues, but did have one notable experience yesterday. I am playing on an original PS4, hardcopy, on an extended drive.
I started with the Revenge in Caviar Key in the SE closest to The Gulf. I wanted to spawn hunter boats to get my Infamy up, so I was using the full Bone set.
I started at Infamy 8 and intended to get to 10. I fought the boats until about 9.5 Infamy. It was pretty choppy by the end. The fight had spilled over into The Gulf, so two zones involved. Other than the fps issues, the notable issue was that it started to affect my sound.
The narrator's voice overs were actually choppy as well. It sounded like a broken speaker. It was very annoying, which is why I disengaged at 9.5 infamy. Even after leaving the fight and waiting for the boats to leave, my sound was still garbled, so I had to restart to fix it.
As I said, I don't pay too much attention to fps issues, but I do notice it sometimes when it transitions from underwater to surface, and when boats are involved.