I don't think there is a definitive guide for best GSync settings yet, but there are some suggestions here. You want to leave the refresh rate at the default "59.950".
Maybe someday there will be an easy On/Off variable refresh rate option when more people have Gsync/Freesync monitors.
Make sure your system folder is set properly in your directory settings on the PC. For changing discs, I think FF8 saves when you finish a disc and you can load up the next and load your save. You can also create an .m3u playlist file as described here. When you load that up there are disc eject and disc next/previous hotkeys you can use to switch discs on the fly. You can set those keys in Settings, Input, Input Hotkey Binds.
Thanks for the link.
Yeah i dont think RetroArch supports any G-sync features which is a shame, MamueUIFX and GrooveMame do out the box just disable vsync and everything works. Mortal Kombat on Mame is a good test, where the character avatars scroll down the side of the screen on the title screen. In MameUIFX or GrooveMame the scrolling on these avatars is completely smooth, but if you load MAME (2014) core in RA the scrolling is jerky so proves g-sync isnt working