[HELP] Best way to config nginx to handle 25k concurrent users from a former Apache guy

Hey all,

I've been using Apache for quite some time on various community sites I've built. I've always used Apache and really enjoy the project to the point of doing what I can to support the ASF.

Now I need to use Nginx for something that would be hard for Apache to handle. I'm about to build something that needs to handle 25,000 - 50,000 concurrent, though very light, users. I have some very beefy servers, both in CPU, disk, and RAM, and network. The server will be serving some very lightweight, custom pages, generated with PHP.

Could you guys make some recommendations on configurations, possibly on a "per 5k user session" basis, or something global to handle 25,000 concurrent users?

EDIT: However, if somebody knows how to configure Apache to handle 25k-50k concurrent sessions, let me know!

Thanks in advance!!