dont know if anyone is aware of the rivatuner use to cap frame rates.
in rivatuner cap fps to 90 and use frameratedivisor 0.
the game runs best and smoothest at around 85-88 fps with what appears to be much faster motions and movements without any of the hyperwalking. Hyperwalking glitches start to happen for me at around 95+ fps.
only issue is remembering to uncap fps in rivatuner when playing other modern games.
Spent first week of diabloIV release trying to figure why the hell my RTX3090ti couldn't get more than 90 FPS on D4
You can however download and run a free program called Riva Tuner Statistics that will let you cap any PC game's frame rate at whatever you want it to be set for. I use that program and set the cap at 65 FPS for FFXI. You could also just set it to 60 FPS, my reason for setting at 65 is because in laggy areas it causes the frame dips to not be as low as when the game is normally locked at the 57-59 FPS.
Yep I mentioned about Riva Tuner in my post lol. You can solve that issue with it capping your other PC games by adding the playonline (pol.exe) file into the Riva Tuner menu and setting the cap for just FFXI by itself. Riva has a global option that will apply the cap to all games, however like you mentioned that causes issues with more modern PC games. So just click the green "add" button at the bottom and you can set XI's frame rate cap by itself and then it won't affect any other PC games frame rates.
For my PC the optimal frame rate for XI is running between 65 and 75. Above 75 frames the game starts moving too fast both with walk speed and attack/spell animations. I'm not sure how it's not hyper running for you at 85, cause it starts doing that on my PC at like 76+ frames. I have an AMD RX 6800XT card which runs modern games really well like Cyberpunk 2077 and Doom Eternal, etc. So idk I guess the XI frame rate varies a little with each person's PC on where the hyper speed will kick in on uncapped frame rate.
Also kinda funny side note, I was messing around and tried setting Riva Tuner to like 500 frames just to see if XI would be able to run at that speed and max it will let you set the frame rate to is 480 on Riva. It actually made my XI run between 390 and 400 frames lol it was pretty insane looking. :P