The game stuttering like that usually means the CPU core the game is running on is hitting 100% usage. You have multiple slow cores in an i7, and the game may be sharing a core with another process. FFXI's primary resource usage is CPU. RAM and GPU are way in excess of what the game asks for, but it can peg a single CPU core easily. FFXI is not programmed to use multiple cores, it dates to before that was a thing. Your best bet is to go through Task Manager and end any process and service you don't need to run the game. Update services and background applications can be doing things that cause the game to lag, unless you learn to specify which core it runs on, and dedicate it just to the pol.exe process. Trim the fat of what is running at computer startup. Turn off things like Google Drive/Steam/OneDrive/DropBox and such if you can.