I'm not familiar with the RX580 so I don't know how good that card is.

First thing to check is under System configuration->Display settings : do you have the frame rate limited here? Mine is set to 60. I use borderless Windowed.

After that its' messing with graphics settings for which there are many references. Here is one: https://www.reddit.com/r/ffxiv/comme...aximizing_fps/