The 1/50 isn't too low a shutter speed for hand holding unless you use a telephoto lens. With flash and if the ambient light is low then the shutter speed won't make a different as the entire exposure is done with the flash that has short duration. The 1/50 is the fastest shutter speed to use with flash on the M6. You can use slower shutter speed if you wish. At ISO 1600 which is very fast film the ambient light would play a rather important role.