If you dont have an Nvidia GPU, dont get gsync.
Yes, you can see the difference between gsync and no gsync. But screen tearing is less noticeable at higher fps. So if you are playing +120fps all the time with a high end GPU, tearing is less noticeable. But if you are playing 60fps or lower, the game play will be butter smooth.
Personally, I love gsync, but it is expensive. It is doubling the cost of the monitors you selected based off of their prices on Newegg. So I dont think that gsync is worth twice as much as a monitor.
Here is an Acer that has similar specs with gsync and is on sale for $350. That is much easier to swallow than the AOC monitor in my opinion.
https://www.newegg.com/Product/Product.aspx?Item=N82E16824009908