1. V-sync causes lag. Don't use v-sync.
2. 60 fps does not mean precisely 60fps/1 frame every 0,0167 seconds.
Here are two pics I made. Both images show the delay of each screen. On the bottom of each pic you can see what the monitor would actually show in each case along with the delay of that part of the screen.
- 60 fps with v-sync
- 60 fps
- 120 fps
in first image the fps and Hz are very well synced. by synced I mean that gpu starts calculating new pic conviniently as the screen just draws the old one the gpu just finished. In the 2nd pic the situation is more realistic with the fps and Hz not being in sync.
The black thick line show the gpu load. Black means full load, red means waiting. With v-sync the gpu waits until it gets the go ahead signal to start drawing again. It basically waits until the display copies the full image from its memory before it starts to work on the new image. Laterally the width of each bar describes how long it takes for the gpu to create one frame. Wider bar means longer time and so forth.
So here we can see the average age of the 120fps frame is about 8ms compared to the 17ms with 60fps.
Here we can see what happens without v-sync. The frames are finished and new frames are started to draw before the screen has "looked" at the frame the gpu is working on. The red dots in this image show the point at which the frame is drawn ("age of the frame" or the lag of that part of the picture on the screen).
60fps v-sync stays as it was because it can not get unsynced. 60fps image gets a tear little below the middle. upper part of the image is 9ms old while bottom is 26ms old. With 120fps we get a tear as well roughly at the same place. Upper part of the image is 4ms old while bottom part is 11ms old.
Notice that unless the tear gets drawn in the same place each time the screen refreshes the screen tear is not visible to human eye.