The resolution in GOS will be changed accordingly with the VM window size.
Enter Full Screen mode, and set "Best for display" in Display settings of Mavericks. Resolution in Win8 should be 2880x1800.
Have you set the Resolution of OS X to "Scaled" -> the last item for More Space? With this option, it makes the display looks like 1920x1200 in HOS, the resolution in GOS will double it, so it will be 3840x2400.