I have been slacking lately as I have been working on my book as well as a couple other small projects, but my average has been one or two a day. I do need to kick it up, as my earnings (or lack thereof) are showing me how much I am slacking. Writing several articles a day comes with time. I find I have to enjoy the topic I am writing about, otherwise I have a hard time producing anything.
When I first started my freelancing career almost two years ago I accepted a 5 article per day position. I quickly found with my other responsibilities I couldn't produce quality with the quantity they expected. I had to withdraw. Plus, they picked the topics and I had a hard time with that.
Typing speed can definitely influence how fast you can write them but you also have to have a plan. As you write more it does get easier; reading also helps as article ideas are everywhere. One just has to know where to look.
I hope this helps, and good luck to you!