It depends on the content and the client. If it's stuff I know and am interested in, and I'm writing for myself, I can produce half a dozen very high-quality articles in a day. If it's for a client who wants a particular subject in a particular style, that number will drop, depending on research and so on. Some writers are very lucky and have a natural ability to pour words onto the page at an astounding rate, while maintaining a reasonable quality level. They're pretty rare, though, especially if the subjects are wide and varied. Most of the time, the people who say they can write 20 articles a day are producing complete crap, fluff filler and articles with nothing to say. I see this an awful lot when I edit content in the self-improvement niche, particularly. So much repetition and "inspiration" (i.e. saying nothing with a lot of words).
As for me, I`m writing 1-2 articles per day, as I need much time to do a thorough research and write in depth blog posts.
I used to work at a company that would hire such guys taking $3 per article, -- the boss wanted to save on content. It was only after marketing dept checked out at time-on-site dropping drastically and readers moving to competitors, when we decided to check out the content, to find it an awful crap with lots of words on nothing.
It depends on what kind of niche you target. If you are in a competitive niche, publishing 500 word articles doesn't mean crap. Google views those articles as less valuable. So to answer your question. I personally publish around 2 articles per week for my own blog and clients'
For a professional writer in our team, She can write 8 to 10 content in 8 hours, New and interesting story with benefits to the audience.
Depends on the subject, which influences the amount of research it takes to get started, the quality needed by the client and how interested I am in the topic. I don't count articles though, I count the words I write and those are 3000-6000 words of an 8-hour writing session.
For an article to work, it has to be engaging enough to read all the way through. Remember how bored the examiner must be after reading fifty exam papers. Make it easier for them to get a good impression about your writing by entertaining them. Add humour, real life or made up examples, or make up quotes.
I can handle 2 600-1000 words a day, but if load is kinda heavy, I can go as much as 4 articles. To create the same high quality for my articles, I just write 2 in the morning, and 2 in the afternoon. At least I have time to rest my mind and breathe, without making my articles dull and below par.
It depends on the quality of the work. I can write around 10 guest posts per day on generic topics, but work that requires more research takes longer, for obvious reasons.