>up-to-the-fraction-of-a-second updates.
I don't think that's true. I believe the comment pages are cached for 1 min.
I've anecdotally noticed an increase in stale pages lately as well, which I would guess is from more aggressive caching. For example, new submissions used to show up instantly, but on popular subreddits may now take a few minutes to show up on the New tab.
If someone really wants to figure it out:
It's like running a tenth of a twitter with a 10k char limit, if twitter had 10 people on development/operations