Raw data flying is based on good scan of parameters and prompt corrections of deviations as they develop so that they do not require major change of flight path. As PF or PM the scan more or less remains same and between the two of them even 10 seconds should not pass without one of them noticing the speed. In SFO accident a training captain and experienced captain under check both never monitored the speed which shows their scanning had deteriorated over a period. Even with full automation the scan is no different. Only that you are passively flying the aircraft. If your scanning is intact you do not need much practice to fly raw data.