Quick note of intro: I'm certainly not a highly-experienced sys admin or developer -- more of a "gifted amateur" as a friend once called me :) Anyway:

I have a large and fairly complex WordPress-based site that's become a lot more popular than expected, and is often close to maxing out my hardware. My challenge in optimizing the site is that all of the most popular pages/files are very time-sensitive -- they're updated at specific times of day, and are very heavily downloaded as soon as they're available. So: I need those pages/files to be flushed from the cache the moment they change, while everything else is cached more aggressively.

I haven't found a good solution for this with WordPress plug-ins such as SuperCache -- they seem to be too "all-or-nothing", flushing too much or too little.

I've been tinkering with Nginx as a reverse proxy sitting in front of Apache. I'm getting very good results so far with regular caching, but I don't see a way to get that "time-based cache granularity" I need. But as I say, I'm no expert.

Any thoughts? Thanks.