*please don't shoot me for this entry; it is simply my opinion*

I think that 300-350 pages is really the maximum size for a novel. And really I would lean to the lower end of that spectrum.

Most of the novels I have read that are 400-500 pages in length would have benefited greatly from excision of whole chapters. The chapter may be a delightful description of the forest foliage through the seasons, let's say, but does nothing to forward the narrative.

I know writers sort of fall in love with certain passages, or with a massive back story that exists for their world building that they've worked hard on to make the novel coherent, but they really need to ask themselves, not "is this well written" because often it is, but "is this necessary to the story; does it truly enhance the reader's immersion in the novel."

Of course there are exceptions to this rule of thumb; though I must admit even the great classics sometimes do go on and on about trivia. The loss of minute descriptions of Victorian knickknacks and their provenance would dilute "Vanity Fair" not a whit, as an example.

I'm not saying that description and/or backstory is bad. I am suggesting, however, that too much of anything (including fight scenes) dilutes the narrative.

So 300 pages (or less) is about right, IMHO.