I'm not an expert, but from what I understand V-Sync on is better. While turning V-Sync off allows your video card to attempt to render very high FPS, in actual fact your framerate is really only as high as the refresh rate of your monitor at a given resolution. So, while it may say you are getting 250 FPS (what your video card is kicking out), you are actually only achieving/seeing 75 FPS or whatever your monitor refresh rate is at your resolution.
The end result of all this according to what I have read is a discrepency between what you see and what your FE actually tells the server happened, this results in the rubber bullet phenomena.
Maybe someone with more technical savvy than myself can articulate the process better. But, in a nutshell turning V-Sync off gives the illusion of better framerates, not the reality of better framerates. Subjectively, I proved that V-Sync off causes rubber bullets, my hit % with V-Sync off is significantly lower than with it on after long periods of testing. Not proof, but evidence enough for me to keep V-Sync on forever.
Zazen
