Having just been playing around with the "Display Options" part at the bottom of the page, I discovered something I'd never found before. The displayed options to alter are:
However there is an additional option that is only available via URL entrance (hence me never finding it before). It is in fact possible to extend the threads-per-page to 200, demonstrated here! I'd like to know if there's a way to change the default on this, the way there is on the 3 above and in-thread posts-per-page.