Dz1on1s :
So basically I can keep my monitor locked at 144hz . Use g-sync. And in game my 90 fps average will sync with my monitor at 90hz? Is that right. Didn`t quite get the answer.
And you suggest me to leave v-sync off, yes?
In that particular use case, V-sync on or off doesn't actually matter, since it can't get to 144hz.
G-Sync controls the monitors refresh rate rather than having it set in advance, so if your system can handle 90FPS it will run the monitor at 90Hz. The key is that G-sync eliminates tearing, no runt frames will make it to the screen and it won't start drawing a new frame in the middle of the screen.
ULMB is a good option when you can consistently stay above 144hz, this will get rid of ghosting at the expense of brightness typically, and tearing is again possible. A good idea on titles that are very dark and have a lot of fast movement.