I understand not to go past f5.6 but at what mm setting is the Leica lens at it's sharpest? I have been told 6.5mm or Z24 but have not seen any test to back this up.
you are referring to the "sweet spot" of a lens. aperture wide open shows aberrations more, closed down affects diffraction limiting, so there is a "sharpest aperture" usually about 2-3 stops from wide open.
everything I've read does not address focal length as a variable.