Average Words per minute in Speech is 130 WPM
in SSB mode it take 2.5 KHz of Bandwidth , so 130 WPM / 2500 Hz = 0.052 WPM/H
in CW mode, it takes 300 Hz of bandwidth, so even at 20 WPM / 300 Hz = 0.067 WPM/Hz
so Bandwidth efficiency of CW and SSB voice is about same.