Everything still working on my side with 38UC99. Though I switched back to 60 Hz because after only about 10 hours of playing at 85 Hz, 60 FPS started to look clunky and it wouldn't take long until I wouldn't be able to play at 60 FPS anymore, which would be extremely unwise considering how demanding 3840x1600 resolution is and how many games were very hard to run for me at more than 60 FPS historically. So I made a bit of a brake from playing and watched a lot of movies in meantime and now 60 FPS feels smooth again and I can fluctuate between 50-60 comfortably, just like planned from the beginning. I am still using V-sync at 60 Hz because VRR implementation is just not good enough to run active all the time without flickering, so I just run locked to 60 Hz (locked 0.010 Hz below exact max refreshrate as per Blurbusters Low Lag V-sync Guide) and V-sync on, and VRR is just in case of FPS drops, and works great for compensating them. I just finished Quantum Break which is extremely demanding and I was below 60 FPS for majority of time and could play through the entire game comfortably, which wouldn't be possible without VRR.
G-sync behavior also changed a bit with newer drivers, restarting the display doesn't do anything good anymore, actually it breaks G-sync, while previously restarting a display would fix frame skipping. But now all you need is to restart the driver with CRU, no need for restarting the display anymore. And since I am running 60 Hz I don't have any frame skipping so I don't have to do anything really, I am only restarting the driver before starting the game because G-sync is sometimes desynced after waking up the system from hibernation.
So in summary I am running 35-60 range at the exact refresh rate of 60.075 Hz, or 59.949 works as well. Plain 60.000 doesn't want to work for some reason (display goes crazy immediately), and by default there is only 75 Hz option with FreeSync enabled in OSD, so I am editing it in CRU. FPS lock to 60.065 in RTSS, Maximum Pre-rendered Frames set to 1 in NVCP just in case, also V-sync Tear Control set to Adaptive in NV Inspector just in case a game wants to enforce double buffered V-sync that locks to half the framerate if it thinks that you cannot maintain your target framerate, like AC Black Flag or Quantum Break do.
MONITOR LG 38UC99 with Ambibox CPU i7 6900K 4.4 GHz GPU MSI RTX 2080 Ti Sea Hawk X 2100/8000 MOBO Asus X99 Sabertooth RAM Crucial 4x4GB DDR4-3000 SSD1 Crucial MX100 256 GB SSD2 Crucial BX100 250 GB HDDs Seagate Barracuda 1 TB and 500 GB CASE Fractal Design Define R5 CPU COOLER Corsair H115i PSU Seasonic PRIME 1200W Platinum MICE Logitech G602 KEYBOARD SteelSeries M800 SPEAKERS Creative Inspire T6300 SOUND CARD Creative Omni Surround 5.1 CHAIR Unique WAU 2 TV LG OLED 55B7V PHONE LG V30