The X100 is a much more capable camera while the M8 is a more versatile, finicky, red-dotted show piece.
The M8 produces beautifully clear and sharp pictures at ISO 160 and 320. I have taken great pictures at 640, 1250 and 2500. 2500 has grain and needs P&P but can look good in certain circumstances even in colour.
The extra DOF provided by the 1.3x of the M8 vs the Fuji x1.5 should also not be overlooked.
Its very fast to use. Finally its a beautiful "work of art" and has alot of owners' pleasure.
The X100 is better for high ISO but not pixel level clarity at base ISO. Its also lighter (although the M8 is lighter then most DSLRs and lighter then all with Leica lenses).
The X100 manual focus is rubbish and its auto-focus is not very fast, so you need to understand the focus system, use zone focus, or stick to non-moving subjects.
Otherwise the handling of the X100 is lovely.
Lastly the X100 is fixed at 34.5mm which is aweful for portraits but ok for architecture, landscapes and "in your face" street photography.
IMHO I would prefer the Fuji with a 50mm equiv.
In summary I think they are different cameras and would be careful to compare them.
The X100 is better when you need something to be pocket size or you are taking close-up street type photography in lower light, for all other things, including a holiday camera, I would personally go for the M8 every time.