This question now has a bounty and this older one got also a good answer on V-Sync.
I feel the newest one should have been closed as a duplicate of the oldest but the accepted answer on the newest is as good as, if not a bit better thanks to the screenshot, than the accepted of the oldest.
So, which should be merged into the other?
The newest question does provide more information than the oldest with links (strangely not of the oldest question... wonder why).