Gsync and Snes9x

[Zazie]

Only works if is disabled "emulate fullscreen". Only problem, with this option disabled, the image is like Mame with option non-integer scaling enabled (bad).

[OV2]

I'm not sure what gsync would give you in s9x, since it has a fixed framerate.
Anyway, if you select the same fullscreen resolution as your desktop resolution you shouldn't see any difference between emulated and regular fullscreen. Newer s9x versions also have an integer scaling option.