The 120WPM is pretty good for the physical limits: if you are typing at 120WPM, then you have not hit the limits of your thinking (imagine you are in a typing tutor—your reading speed ought to be at least 3x 120WPM...), and you’re not too far off some of the sustained typing numbers in https://en.wikipedia.org/wiki/Words_per_minute#Alphanumeric_entry
The 120WPM is pretty good for the physical limits: if you are typing at 120WPM, then you have not hit the limits of your thinking (imagine you are in a typing tutor—your reading speed ought to be at least 3x 120WPM...), and you’re not too far off some of the sustained typing numbers in https://en.wikipedia.org/wiki/Words_per_minute#Alphanumeric_entry
My point was that 1 bit per character is an underestimate.