After making the above change, xrandr in the guest now returns video modes with resolutions up to the size of the VirtualBox window, and when I go to full-screen, I can use up to the maximum resolution possible with my monitor.
After making the above change, xrandr in the guest now returns video modes with resolutions up to the size of the VirtualBox window, and when I go to full-screen, I can use up to the maximum resolution possible with my monitor.