One thing I learned this month is that I am capable of writing four thousand words a day - not much more than that. At the 4000th word, I get loopy and my story starts going in strange places. And then for two days I don't want to write. And there's no amount of encouragement or positive energy anyone can throw me that will make me want to write.
It's kind of like eating a quart of ice cream in one day or at one sitting (not that I've done that). I would enjoy it while I was eating it, but there's no way I would want to have anymore for a very long while.
I definitely prefer writing at a pace of a chapter a day, 1000-2000 words. That is definitely more sustainable for me.