I have absolutely no idea. All I did was just open the custom resolution box in NVCP running latest drivers, type in 3840x1600 120 Hz in its boxes and add it. No timing changes or anything. NVCP is also set to use display scaling, setting it to use GPU scaling might help as it would then create 3840x1600 on the GPU and output it scaled to 3840x2160 with black bars. Same end result pretty much.