The M8 (and any lenses) are significantly heavier than the X1 if that matters to you. And as BB says you have to manually focus which I too can no longer do easily. If it were an used M9 and weight and focus weren't an issue, it would be a no brainer because of the full frame sensor. But, the M8 has the same size sensor as the X1 so it's not an easy choice. I went the X1 route and I love it but it has its limitations.
First of all, I completely disagree with usayit's saying the X1 is a point and shoot unless we call all sorts of other cameras the same. :