I know that when I played Minecraft around 2 years ago on a 20" monitor, Large GUI and Auto GUI were the same thing. Then I upgraded to a monitor that had 1920x1080 on it, and Large and Auto GUI had a significant difference. I know that playing on a 2560x1440 Resolution, the GUI starts getting smaller than what it had before. You will be able to see more of the screen by just a fraction if you're playing on Normal FOV. But if you up your FOV to something like Quake Pro [not recommended] Then you will be able to see a lot more of the screen than you could not playing in 1920x1080 or 2560x1440. I don't think that resolution would affect the performance, as long as you're able to run it.