I test your script and compare it on my LEB with my common setup.

- OpenVZ 128MB RAM

- Ubuntu

- Nginx

- MySQL

- PHP-FPM

- APC

- Varnish -->> Redis

At 250user/second here's the result : http://imgur.com/a/hPkyZ

This is vanilla WordPress installation. There is almost no difference in load time or overall resource usage as far as I'm concerned. I've never use Redis before so thank you for this.