on xda some were saying 1440x1184 but
the correct size is indeed 1440x1280. i have some loaded on my phone now and i'm able to select the entire picture.
further evidence of this being the correct size...
/data/system/wallpaper_info.xml says 1440x1280
edit: the 96 pixel diff is because of the software buttons. what this means is that the correct sized wallpaper at 1440x1280 is being cut off by the software buttons at 96 pixels. with this being said, to view an entire wallpaper without any being hidden by the software buttons, you'd need to crop an image to 1440x1184 and then add 96 blank pixels to the bottom. hope this makes sense.