iftop was showing me a pull of 110-140Kb/s, with only one connection, so the
throughput ratelimiter might need some tweaking.

I could, of course, block access to some of the dynamically-generated pages
(page history is probably the worst), but I prefer not to, and it's rare that
it's a problem.

The site's already as optimized as I can make it, short of using Squid--but
MediaWiki requires a patched version of Squid that recognizes a few unusual
HTTP headers, and that's not something I want to mess with. All in all,
though, I didn't come for advice on configuring the server, but on what types
of rate-limiting components I can put in robots.txt.

If someone chooses to override robots.txt, and it causes me problems I notice,
I can go draconian, but I'd rather give the benefit of the doubt.