I did some statistics a few days ago about the fanfic novel I completed and posted on the Internet. From the day I started writing until the day I completed it, I wrote on average 3623 characters per day, that would be approximately 671 words which is almost exactly halfway 500 and 800. I voted 500 in order to not appear too pretentious. But I didn't strive to complete it as quickly as possible. In fact, I had to force myself to not spend too much time on writing, because of other more important things. On the other hand, it was only fanfic. Had it been a real novel, I would have surely been slower.