Well it depends. If the content is helpful, unique and answer questions that the reader may have, then a 300 word article works just as well as 800 word article. Now if the content is related to violence, nudity such as flashing people in public, or anything related to drugs, then 800 words is a must!
Ok, so what I'm understanding from the posts here is that it may have a slight affect on SEO Rankings. But what does the content matter if it's helpful or quality? Like isn't that something only the website visitor would be able to tell? Like how could Google measure if the website is not helpful or is content is not quality.
That is why you have to write for both the G bot and your readers. The long articles (800-1000 words) are for the search engine. The medium-length supporting posts (250-500 words) are for both, while shorter posts (150-300 words) are for your users. Shorter posts should be n0-indexed if there are too many.
I can tell you this, I've had sites that stagnate at the top of page 2 or bottom of page 1. If I add more well written content they usually get a bump in rankings. It's not always permanent.