The only difference is that the monitor would pull much more power from the wall, but the GPU output is identical, assuming the monitors take the same exact connection, are the same panel type, and are the same refresh rate. Even then the difference is probably less than 0.1 of a frame, if not a fraction of it. If you took a 30" monitor and put it through that chocolate thing from Willy Wonka, it would be the exact same.