First of all, there's no such thing as 18GHz. The GHz don't sum up. It's like saying that if a woman makes a child in 9 months, two women can make a child in 4.5 months. It doesn't work that way.
Moving forward to the actual issue. Something is really broken into your configuration. The first thing is the file AIO. But this is Linux's fault. The file AIO is broken by design. It bypasses the kernel file cache. Which is a pretty large performance hit per se. The second thing is the fact that I can easily get 55k req/s on a Q9400 with nginx, without even touching the sysctl parameters of a Ubuntu 10.04 x86_64. The only actual difference is nginx 1.0.x instead of the ancient 0.7.x you would actually find into the standard repos aka the production version I publish into my company's private repo.
Moving forward to the actual issue. Something is really broken into your configuration. The first thing is the file AIO. But this is Linux's fault. The file AIO is broken by design. It bypasses the kernel file cache. Which is a pretty large performance hit per se. The second thing is the fact that I can easily get 55k req/s on a Q9400 with nginx, without even touching the sysctl parameters of a Ubuntu 10.04 x86_64. The only actual difference is nginx 1.0.x instead of the ancient 0.7.x you would actually find into the standard repos aka the production version I publish into my company's private repo.