Fact: If you have to defend that your novel is over 200,000 words in your query letter, then you are not pitching your story from a place of strength. And agents are more likely to pass.
Even though a writer might insist that the length is necessary for the story, rarely is this true. In fact the hefty manuscript getting picked up and sold for a debut author is so rare and unusual, industry folks make note and remember the titles (i.e. The Story of Edgar Sawtelle and Jonathan Strange and Mr. Norrell).
In probably 99% of the cases, a super long manuscript usually signals that a beginning debut writer has not mastered pacing. Or, that the writer has not learned self-editing. This is even more true when we talk about the fantasy genre. Lots of fantasy authors will cite George RR Martin’s Game of Thrones in the query letter. A great example certainly, but that wasn’t George’s debut project. Most established and successful fantasy writers begin with a normal length debut (around 100,000 words with some room on either side of that).
And yes, you can certainly cite the extraordinary instance of Patrick Rothfuss and The Name of the Wind. But he’s an exception, not the norm.
So my advice? If you have a long manuscript and you truly believe it is the “one in a thousand” and is the appropriate length, I wouldn’t cite your word count in the query and instead focus on writing the most incredible pitch you can.
After all, if an agent/editor begins reading and is blown away by the mastery, we won’t care a fig about word count. We’ll believe. But you have to get a request for the pages first.