This is one of the worst misconceptions in the science of computer purchasing.
Gaming should not be a reason to choose a 15.6" 1366x768 display instead of a 15.6" 1600x900 or 15.6" 1920x1080 display, or to choose a 17.3" 1600x900 display instead of a 17.3" 1920x1080 display. For one thing, you can always make up for drops in performance associated with higher resolutions by lowering to a non-native resolution, but you cannot as easily make up for the limits imposed on multitasking by a lower resolution.