Just coming back from there.
To make your ROG 751 start faster you have to prepare windows 8.1 installation USB using GPT partitioning (UEFI boot). Ask google USB boot windows 8.1 GPT. When USB is ready start and hit "esc" until you get to select boot device manager... Its imperative to select UEFI: USB model from the list. After that windows detects that pc is using uefi and done.
Make sure that CMS (old systems partitioning) is disabled.
Had same issue win 8.1 starting from SSD for around 16-20 sec, now after GPT (UEFI) install it starts for like 2 sec and its showing ROG logo as boot.
Return this notebook...
See my video, look at the description how many people here in the forum with same problem.
No solution from asus.