The one time I was tested, first and only time I ever used a Selectric Typewriter, I did 35wpm with zero errors. I would guess that on the computer when I am writing I do about twice that but I do not worry about errors when I am trying to get ideas down. One of the problems I have is that when I watch the screen I keep stopping and correcting errors as the happen. That blows the line of thought and I wind up sitting there staring at the screen wondering what I was thinking of. Sometimes, to prevent, that I will close my eyes while spinning out words. I imagine a lot of folks look at the keyboard when typing for the same reason, but I find that slows me down too. I would guess that writing something like this post where I am trying to edit as I go that I only do 20-25 wpm.
A side note: traditional typing tests test transcribing speed (copying text), they do not test creative writing speed.
BTW, does anyone besides me find that all that help, programs like word give you just gets in the way of getting words down? I really have never found anything I liked any better than the old DOS program Q&A Write for that.