Can you elaborate on the GSync? I have one and my game still kinda stutters.
Essentially... G-Sync and Optimus are not compatible. In an Optimus setup, the video output is always being run through the Intel graphics. The nVidia GPU is more of a co-processor that the displays are never actually connected to.
Meanwhile... G-Sync requires communication between the nVidia GPU and proprietary nVidia chip in the monitor. Until recently, only over Displayport. Other variable refresh setups are similar.
Tl;dr, a laptop doing G-Sync is connecting the display(s) directly to the discrete GPU by necessity.
It's still possible that you have other performance issues with that sort of setup, it's just eliminating the common hurdle of switchable graphics just using the Intel graphics.