The key answer to your question is: the same lens will have different focal length in M8 and M9. This is caused by sensor size difference.
50mm lux on M9 and M8
The M8 has smaller sensor than M9, which means focal length for lens is different.
Examples:
50mm on M9 = 65mm on M8
35mm on M9 = 46mm on M8
M9 ISO performance > M8 ISO performance
M9 dun need special filter for colors, M8 need special filters for color correction
M9 bokeh > M8 bokeh (due to sensor size difference)
M9 LCD made of scratchable plastic, M8.2 LCD glass made of sapphire glass
M8.2 has the following features that M8 does not have.
* A new extra-quiet, low vibration metal blade focal plane shutter
* An ultra scratch-resistant sapphire crystal cover glass for LCD
* snapshot mode
* A “vulcanite” finish to the camera body (black and silver versions)
* Viewfinder bright-lines (to frame subject) optimised for 2 metres (M8 is 0.7 metre)
* A more compact, faster charger
M9 has all the above features of M8.2, except the LCD sapphire glass. M9 only got lousy plastic.