Possible Clues:

• More intelligent
• Always after a century and a half, always with 'er one is more than smart
• Top off container, one pulling on handle quicker?
• Less dense
• A hundred and fifty could make one comparatively smart and always with 'er
• More than smart with fifty always inside
• Mentally quicker
• Always between 150 and 'er to make this more smart
• More shrewd
• More resourceful