Optimizing and problem solving nginx+PHP-fpm installation running WordPress and vBulletin by androidnorth

I need a complete rundown of our nginx+PHP-fpm+apc+memcached configuration running on top of Ubuntu 12.04 (VPS). We are experiencing both stability and performances issues. Requirements: *Long experience… (Budget: $100-$450 USD, Jobs: Linux, Nginx, PHP, Website Management)