I am glad you asked this question because I've been wondering myself.
Years ago, the wisdom was that articles should be between 400 and 800 words. Back then, anything over a 1,000 words was considered off putting.
But that was back before articles became multi-media extravaganzas. I know that on the Learning Center page it reads that 1,500 word articles are one of the marks of a stellar hub. I think, but don't know for sure, that that is probably because it takes at least that many words to make the formatting look proper and proportionate to all the media one needs to make the article engaging.
I think too that perhaps due to the Google changes, one's rank is now based on considerations other than just SEO such as the length of time a reader spends on a page.
However, I do wonder how much is too much, so thanks again for asking.