On a full size keyboard? Most veteran typists can put down words at or above natural speech rate, especially the somewhat slow and stilted speech that seems to work best for those dictation software packages.
(Short answer = that depends...and software like Dragon has many other advantages/drawbacks that factor in.)
"For myself, let’s compare typing vs dictating, given the above information and a 1,000 word email.
Straight typing: 90 wpm = 11.11 minutes, no proofreading allowance, correcting errors as typed.
Dictating with Dragon: 140 wpm dictating (7.14 minutes) + 300 wpm proofreading (3.33 minutes) + correcting 10 errors @ 10 seconds each (1.67 minutes) = 12.14 minutes.
For an average professional, typing speed is rated at 50 wpm. A 1,000 word email would take approximately 20 minutes to type.
For an average professional, their dictation with Dragon stats would approximate my own (12 minutes) — they are not unreasonable."
When dictating, you also hit the classical problem of your thoughts not forming fast enough to be able to formulate yourself in writing in real time, leading to a lot of breaks as you dictate. The guideline "think, then speak" of radio communication also holds for dictation, in my experience.
*more keystrokes but same time spoken, as the natural speech cadence is faster. Can't remember source right now.