I actually just purchased an X100s a few weeks ago, so i can give you a hands on compared to the 5D Mark III
If you shoot mostly in the 24-50 range with your 5D, then you will like the x100s alot. If you shoot mostly 100-200 then you will miss the bokeh and seperation from the background. With the X100s you have to open it wide open and get pretty close to your subject for any shallow DOF. The x100s colors and sharpness, i think are excellent, especially skin tones. The camera is a little quirky. If you are trying to take pictures of moving things like sports and kids, it's hard... See my sample pics attached...
Nice pics and I love the IQ. Much PP on these?