If you just play FFXI and sensitive to change I would wait. You also have to be ready to learn a bit. If you decide to try it out, do a clean install on a freshly formatted hard drive. You are more likely run into problems doing the upgrade, this has always been the case with Windows unfortunately. I suggest on a separate partition or drive.
Some people have problems with FFXI on Win8 or more specifically windower.
http://www.ffxiah.com/forum/searchq=windows+8&view=topics&sort=1&date_range=1
I have it installed on my main PC. I was using new SSD as a coaster for while and decided it was a good time to plug it in. I will list some observations I've noticed.
Goodies
You can use a Microsoft account to log in, which allows windows to sync user settings and wallpaper etc to other Win8 devices. It has better dual monitor support as far as spanning wallpapers and customizing the task bar. The task manager finally does not suck.
Touch Pads
/facepalm, it supports gestures as if the touch pad was a tablet. I don't think this is a good setting by default. You can disable it by finding the settings.
Apps
Win8 has "Apps" and their ecosystem is very young... well let's just say it sucks so far. Common files are sometimes associated with apps, this can be very annoying for a desktop user. You can change it as this occurs if needed. If you accidentally start an "App" and wondering where the close button is, it's Alt+F4.
Stability/Speed
Windows 8 boots faster than its predecessors, I think most agree on this. I never had a blue screen or had to restart besides windows updates. FFXI works fine for me, just have to make sure to run as admin. Games run about the same as 7.
Start Menu
I hardly use the new tile interface. I go straight to the desktop, WinKey+D is your friend. Also WinKey will take you back to the start menu. You can use
http://www.classicshell.net/ to get the old start menu back if you desire. I personally have it installed but never really browsed for programs since index searching on Vista (yeah, I used that). I think the new start menu is nice looking but I don't have much use for it. My wife has a windows phone (HTC 8x) and the interface is nice and easy to use(I still prefer Android).
tldr;
It's much like Windows 7, except the start menu is full screen tile interface. It would probably get more use from a touch screen. As a desktop user, you aren't missing much if you have 7. I think they should of set up profiles such as "desktop" or "tablet" and establish some default behaviors. Although it would feel a lot like 7 on desktop mode. Overall I've had a positive experience. Use
http://ninite.com/ to get up to speed after a clean install.
My desktop
https://dl.dropbox.com/u/13941904/Screenshot.png