Chromebook Pixel is 3x2.
5x4 is a really awkward and (imo) stupid aspect ratio. It has some really stupid reason for existing relating to limited VRAM in the 80s and traditionally had non-square pixels on CRTs. Seeing as its reason for existing was already obsolete before there was even such thing as a desktop LCD, why 1280x1024 desktop LCDs exist is beyond me.