Nginx+php-fpm optimization for high performance

We are looking for a professional that help us to tune up and balancing our nginx server and php-fpm we use nginx+php-fpm as webserver and Xcache for caching system It serves dynamic content and gets crash continously twice/hour and makes visitors to see 404 error when php-fpm crash/respawn,, thats the problem we need to fix. More than giving access to our server we are looking for a freelancer that can tell us what to check or what to modify, we will provide all the needed server details/info. the lower bid and more rating freelancer will be priority.