Valent - this doesn't increase your performance at all! All it does is remove the sync between OpenGL drawing and your screen refresh. It is likely, for most people, that this will cause (increased) tearing on video. I do not agree with that article at all, I would strongly suggest that you turn it back on. The only real performance issue you will get with vsync is the video driver not using "events" to control resources during idling for the sync. The use events option in your xorg.conf file will correct this - but this option is standard for all the recent versions of nVidia's drivers anyway, so you should be good.
Perhaps looking at it this way - vsync effectively hides the performance of your GPU from a frame rate tool like glxgears, because it forces the GPU to wait between frame draws until the display's sync period when it is not drawing anything... in this way it avoids tearing. The GPU itself is still drawing at exactly the same rate as before... that is why your first figure is exactly 60fps... because your display is 60Hz refresh!
BTW, when not sync'd, a figure of 510fps is pretty low. What GPU are you using? And have you confirmed that the xorg.conf file is using "nvidia" as the driver?