X100 F4.0 sharper than F8.0?
Sometimes shooting with a shallower DOF gives an image more apparent sharpness than where more is in focus
I do believe f4 is the peak sharpness of the lens, but I've never found F8 lacking at all. Diffraction probably sets in pretty strong by F16 given sensor size
I wouldn't hesitate using F8 for landscapes etc though. I'd rather have the DOF that every last line/mm resolution at f4 and not have everythign I want in focus