How much editing is too much?

I wouldnt worry as much about word count. For a WWII book, I can see 200k words easily. What I would worry about most, is the context of your overall plot. Does every scene carry the plot forward or develop a character? Can more be cut? There is no magic number for how many words should be cut. If you're satisfied with the book from beginning to end... it sounds like it might be ready for beta reading, time for some feedback. =)

Don't worry about word count. Instead, focus on making this the best book you can write: prose, narrative, characters, plot, subplots, themes, etc. Make every word count. Cut the words that don't.

When you're done and find yourself tweaking this and that with nothing "significant" to change, then you're finished. Time to submit.

I would agree with Maestro...sorta.
If you're writing a sweeping WWII saga reminiscent of James Michener or Diana Gabaldon or Jean Auel, then, yeah, word count's not so much of a problem. If it's a romance set against a WWII background, then it is.

Having said that, I doubt Michener could get published if he was starting out today. Who knows about the other two ladies? I've read many agent blogs where they say they won't look at a debut novel much over 100,000.

I went through a similar odessy with one of my novels. Each time I went after it, I hacked away another 8 - 10%. Do that often enough and you eventually get where you need to be.

Final thought: Maybe it needs to divided into two or three successive books. Check out Herman Wouk's Winds of War, etc. He always wrote long, but still made a series out of it.

I'd be making sure everything is in the story that has to be there and that it reads well. Leave it for a while and come back to it with fresh eyes and read it straight through. Have you cut something out that should be there? Or have you cut something out and there are references to that subplot elsewhere? I'd concentrate on the work rather than the word count.