We've been running Nginx for sometime powering a fairly high traffic website. The single box, dual CPU (dual core) has been serving us well but its time to upgrade. I've got a new system configured, quad CPU (quad core) = 16 cores (plenty of RAM) and CentOS. My understanding is that even though there are 16 cores, more than 5 Nginx instances will not greatly improve performance.

I decided to benchmark the system using a single Nginx instance and default configuration with a static html file. Using "ab" (locally) with 50,000 connections and 1,000 concurrent ones I get around 10K requests / second.

What particular parameters should I look into adjusting to try to double that number? (Nginx and OS).

What is considered top performance for a single box / instance?