140wpm is extreme.
I'm at 95wpm, no mistakes, and 108 with mistakes. 20 years of typing will do that to ya
But typing speed and content writing speeds are totally different. I can spend 10 minutes typing a 250 word article and another 15 minutes tweaking it for SEO and links etc as well as grammar changes. It all depends on what the end goal is about.
By the same token, I fly through forum posts here and other places daily without any mind for SEO. While I am not to be as careful on forums regarding structure and going off track on tangents, I do try to proofread my posts for grammar and spelling and overall content before clicking post.