My g-sync experience is that its hardly noticable when maintaining high fps in games. Many people come from 60hz monitors, to a 144hz g-sync monitor. Then they think that the g-sync is the reason for the ultra smooth gameplay, when its really the 144hz that does almost every bit of it.
I came from a 144hz monitor when i tried a g-sync one with 144hz. The difference was so small, that there is no way i will pay the premium price Nvidia is asking for these days. I therefore went back to my BenQ xl2411t, and i have not missed g-sync at all. Its nice to have, but not paying that kind of extra money for, in my opinion.