The Intel HD Graphics 3000 supports up to 2560 x 1600 through HDMI, VGA and DisplayPort screen resolution. See below for information about graphics specifications:
Please bear in mind the graphics controller can support up to 2560 x 1600 but computer manufacturers may disable some video modes
2560x1600 is only supported through Displayport as far as I know. HDMI/VGA only up to 1920x1200.