texture resolution is the next Vram hog after overall game resolution.
i had a Korean (Shimian) 2560x1440 ips for around 3 years. i don't notice the lag at all. i'm not sure what the shimian was rated at but i'm certain it wasn't much lower (if any) than this Samsung. i tried "game mode" with the 20ms lag and "pc mode" with 34ms. i just leave it in pc mode even gaming.
Maybe I have something set wrong then? I used the edit input function to select game mode and in special viewing or whatever it's called it says game mode on and I can still feel the somewhat lagy mouse input. More in some games than others. I mean it's not terrible mind you but my Catleap at 100hz was better for sure.