>At least with numbered pagination you can choose to view page [whatever] to narrow down the posts you want to view
Assuming you mean sequentially, isn't this the same as scrolling but with a click involved? If you don't mean sequentially, how would you know which page to click?
>If I know something useful is on page 10...
How do you know something useful is on page 10? Is it normal for forum users to remember specific page numbers within a post?
I also like page sizes as "breaks" to follow up on links etc.
Discourse's implementation of infinite scroll isn't all that bad (it keeps position properly and doesn't seem to have strange glitches, although I haven't tried it on a bad connection), and at least navigation elements are there. But they feel strange and trip me up every time: the secondary "scroll bar", or in thinner browser windows the "progress bar" at the bottom that overlays the post content and you have to click to get the scroll bar pop up. It feels like a mobile app, half-way designed for touch, not a forum.
If I know something useful is on page 10... well I'm just out of luck.