I don't have extensive comparison between Fuji and Leica M, but there are a lot of comparisons between Sony A7/A7R to Leica M.
The differences are dramatic, with the same Leica M lenses of course. In general it is not recommended to use lenses cross the system.
When each uses its own native lens, you get typical Leica M rendering vs. Sony rendering, which one is preferred is subjective.
Between Sony A7/A7R and Fuji X? Not meant to start another endless debate, but you should find a lot more preference towards A7/A7R.
The bottom line is, you should ask yourself, is Fuji X good enough for YOU and if YOU are willing to pay the price difference? If you are not sure, usually the answer is very clear.