We have a magento ecommerce with 10k visits/day.
We have tried to optimize it at maximum:
- Nginx, Varnish, APC cache php-fpm
- Huge Hardware with:
3 different machines for database, varnish and php
The problem is some php process that eats CPU and the load goes up sometimes with no reason (even if we have few concurrent users).
You have to detect wich could be the problem and, by the way, optimize the things you notice. (install fooman speedster, fix the Yslow and pagespeed requeriments... etc)
We can set an hourly price to check the things you see that need fix and then giveme the final price/hours to fix it.