Soon to be Finished: Book 5

My goal for book 5 is 250 thousand words. I am at 238 thousand and the story is just entering the climax (update: 250000 words reached July 12th). The last bit of book 5 is just about to be finished and soon I will have finally finished the first draft. It is already longer than any of the others at almost 500 pages in reading format.
Despite this, I have not yet finished book 4. I have books 1-3 completed (first draft) but not book 4. Why? I started books 4 and 5 at the same time under the idea that both could be written at the same time, that when I ran out of ideas for 4 I could work on 5 and vice versa.
But there was a problem with that. I loved book 5. I love all my works but book 5 really drew me in like no other story had. It was what book 5 was about that drew me in. Its themes have helped shape the way I look at the world and the emotional themes were so powerful that sometimes I would just stand up and wander the house while thinking about what I've wrote or just lie back in my chair. Sometimes I really upset myself when writing the sad scenes, I really did! Of all my works book 5 is my new favourite.
Despite its length, importance to the storyline, and strength, book 5 is the only one (so far) that I will not discuss on this blog. It gives away too much about what eventually happens during the other books. I have personal ban on publishing material related to book 5 here. In fact, of all the excerpts I have in my excerpts posts, only one is from book 5.
Now that I am coming close to the end of book 5 I can do one of two things. One, I can start book 6 which I have already named and made a cover for. Two, I can finish book 4 which I haven't worked on for months. Three, I can start book 6 and work on it when I feel like it while focusing on book 4. I really got to finish book 4, I really do.
I look forward to writing the second draft of book 5. It would mean I get to read it.