Ok.. I found the answer on page https://rog.asus.com/forum/showthread.php?61399-Overclocking-G551JW-with-GT960M 

Hi. I bought G551JW a week ago and Witcher 3 this weekend. The game works tragically  I try to play in low details in 1366 x 780 resolution and it doesn't work smoothly.Can you tell me Piro:1) have you update graphic driver (if yes, then from nvidia...