G-Sync Help?

Hello all,

Just have a few questions about the up coming g sync from nvidia. Basically, I saw one of the demos and it was playing a game at 40fps and compared it to 60fps on a v sync monitor, and both were just as smooth. So, does that mean that g sync allows frame rates to always be butter smooth or am I missing something here? I want to eventually get the Asus rog 27" 1440p g sync monitor and I have a gtx 780 for graphics. With g sync, does that mean even if I am getting like 30fps or something will it be like 60fps on v sync?

Peace and love,

Gmasstaa

 here https://www.youtube.com/watch?v=fghQh0Y4oA4