No! Never slow down! Anything beyond 50,000 words by the end of November is great, anything less than 50,000 isn't so desirable ;)

Plus, I've heard that the second week of writing is the most difficult one to get through and many people get discouraged, so it's best to have a word buffer just in case that happens to you by your second week as well. It hasn't happened to me (yet? I started a bit late as well, haha,) but it's a very common phenomenon so I'd make sure to keep writing while it's easy!