What's so good about 800, and why are you SCRUBS using 15 posts per page? My god, you probably use top postbit as well.
40ppp all day
this seems accurate... until you try to optimize it even more. I happen to like the revolution skin, but it has this problem where it wastes lots of sideways space. However, this is relatively easy to fix with simple greasemonkey scripting.
Here's where the posts/page comes in. The fewer posts on a page, the quicker the page loads and gets the right width, so it's faster to start reading something on a 15 posts/page setup.
Furthermore, while I'll admit that 40 Posts/Page is more efficient for reading through many posts at once (i.e. if you're an infrequent visitor), but for someone who checks frequently, it's much quicker to figure out the context of the new posts when there are less per page (pages are more likely to have coherent topics, where there's more drift/ page on 40 posts/ page).
tl;dr: for people who want to maximize screen space and reading efficiency for frequent checkers, 15 Posts/Page is actually more efficient than 40 Posts / page.
For everyone else, you are scrubs for not using 40 posts/page.
P.S. Top postbit is ********.
edit: hope I don't start any fights about who gets post #12000
