I've seen 250-400 words quoted as the ideal length but I've seen no evidence to suggest it would actually be harmful to have more content per page than that and I can't see any reason why it would hurt. I would think that 250-400 ought to be the minimum.
I have seen these 400 words quotes as well, but some SEO sites use very long text. E.G. the bruceclay.com used to be at the third position for search engine optimisation before recent algorithm change (more weight on anchor text).