If I know about the subject, then I can do about 4-5 quality articles an hour. If I have to research on a topic that I'm not familiar with, then will probably be 1-2. I can work all day, so if I need to write for someone else than I'll find a way to meet the request for content.
I use dragon naturally speaking, I can get a new article every 10 minutes (500 words). The first few take some time, then I just go off memory and speak quickly. If you are trying to beef up your blogs without outsourcing, just find a copy of DNS and learn it. Takes 10-20 minutes to get the hang of it. After that you become an article machine!