A 27" Gsync TN panel would take you into 16:9 aspect ratio panels geminireaper. All in what you wish, though I assumed you were set on a 21:9 aspect ratio with looking at a X34 Predator.
If you are coming from a 120Hz + panel, the 60-100 Hz(100 with overclocking--IF successful on that panel..not all can reach that speed) May feel a little less fluid, especially at 60Hz, regardless of Gray to Gray response times. If you are used to 60hz, not an issue.
The Gsync does help greatly with less than 60Hz framerates for eveness of frame pacing. Even with a 1080 ti, you will probably appreciate this more with certain titles that will struggle to reach 60 FPS at Ultra settings. To most people, that is MUCH more noticeable than 1ms vs 4ms...