The text size, number of posts per page, etc. are constants and are not changeable through manipulation of the URLs. Right now there are a couple things you can do, but they are mostly bugs that are waiting to be fixed, such as the ability to circumvent the depth limit with undesirable results.
One thing you may find useful, though, in threads that span multiple pages: At the end of the URL add &start=250, replacing 250 with whatever post number you want it to start with. That could be helpful if you want to view a specific subthread that would normally span 2 pages, enabling you to view all posts in the subthread at once.
John