Just my two cents worth after carrying on duty, off duty, concealed in various different locations.
From an untucked shirt concealed carry, I think the fastest you can do is from inside the waistband, near the center (belly). This is with a open top holster IWB. I think this is based on economy of motion. One hand has to lift the shirt while the other brings the pistol into action. By moving both hands to the centerline, I think that economy of motion is maximized. With a tucked shirt, at least one of the hands, cross draw or strong draw, has to move completely across the body.
When carrying open, I believe a strong side, mid rise OWB hip carry is your fastest. This is with no retention device such as a thumb break. The legendary fast draw peace officers like Bill Jordan and Jelly Bryce carried in this fashion. Both could draw and hit in under .4 of a second. There are others who have come after them with similar skills with the same type of set-up.