This would also be the longest book I have read. I'm also currently reading A Game of Thrones which is pretty long.
I just started book one of Game of Thrones myself.
Longest single book would be Harry Potter 5. I read that whole series. However, I read all 4 Twilights in 4 days and then the first 7 House of nights in one week if those wanna count as one per series. Haha.