What are the under-documented differences between iPhone 8, iPhone 8 Plus and iPhone X? Besides the differences called out by Apple's comparison site such as price, display type and size, telephone camera, TrueDepth Camera, and Animoji, what are the differences between iPhone 8 and iPhone X?
iPhone X has a 120 Hz touch  sample rate. 
iPhone X has a 10 channel true tone sensor and the iPhone 8 has a 4 channel sensor.