Dean Wesley Smith wrote a good piece on his blog about writing speed, quality, and productivity. I definitely recommend reading it if you have the time.
Writing Slow Equals Writing Better is a complete myth, a nasty sacred cow of publishing that hurts and stops writers who believe it.
— The truth is that no two writers work the same and no book is the same as the previous book or the next book.
— The truth is that writing fast is nothing more than spending more time every day writing.
— The truth is that there should be no rule about speed relating to quality.
— The truth is there should be no rule that lumps all writers into one big class. There should only be your way of writing.