So I said I'd post every duty that it happens in, but it's been happening regularly enough now even with Listening Position at 100 that I would go crazy if I did that. It'd now make more sense to list what duties it didn't occur in with Listening Position at 100.
And indeed, reading that quoted post was VERY interesting:
I took a look at FFXIV's CPU usage when stuttering was happening (Intel i7-920, 2.67 GHz), and I noticed it would go to about 40-50, when normal usage is about 18-25. However, I wasn't getting FPS drops. So this must be what's happening for me. It also seems to happen more often around Sage actions, but then not always. Maybe Dancer too, can't really tell. One thing that I think has helped me a little is changing Battle Effects to Limited or None. This is inexplicably found in Character Configuration->Control Settings->Character tab. This is incredibly undesirable, but I can at least tolerate Limited for Party and None for Others, for now.
However, my biggest problem is that even when it's not stuttering, even if that is fixed, the audio is still wrong. All of the audio is just off, and it's not the fault of anyone's computer. It's just that the sound engine is incredibly poor and playing it all wrong. I don't know what much else to say about that. The sound engine was perfect in Shadowbringers, then plain ruined in Endwalker. I simply didn't realize it until I started doing pre-Endwalker duties again and hearing how obviously wrong it all is, such as in the Nier raids. This isn't some hard-to-grasp issue at all. You can hear it extremely easily on any computer. Even when the audio's working, it's just very obviously wrong in 6.0.
And I take back my concern that Endwalker's audio is unique to this sound engine and so they literally can't revert to 5.5. The benchmark proves that's false because it had plenty of Endwalker audio in it and it was very obviously on the same, good old sound engine that worked perfectly. So there should be absolutely no way that the 5.5 sound engine can't be provided for us, the players, in Endwalker. And if the response is that it can't be an option due to technical reasons, we will know something went very seriously wrong because the benchmark was fine.