Its not a good idea to show more than 1 page of content in a single web page. You definitely do not want to show 300+ pages in a single web page. If you want to give them all that at once I would create a .pdf file and let the user download it.
In the future I plan to add support for pageing into the Html Content feature so that you could define pages within an article. Still, 300+ pages is more like a book than an article. Very unliikely that anyone will ever read all of it in a web browser. With a .pdf the user can download it and read it without being connected to the web and/or could import it into a reading device like the Amazon Kindle.
If you're going to publish a lot of large documents I would go with the .pdf approach. You could either upload a .pdf to your server and link to it, or use the mojoPortal shared files features to upload and share it.
Hope it helps,