I'm not convinced that an un-separated guide is helpful (I have no problem with a single page but honestly, pages are cheap so a landing page that links to N900 and pre-N900 guides makes the most sense to me).

The considerations are so different between N900 and pre-N900 that you'd end up with every section having two parts. Even the choice of encoding software isn't clear - Handbrake is a good fit for the N900 but as the newest version has only very basic xvid support, it's unlikely to be the right choice for the older models.