Impact of Zend Optimizer on PHP Performance
The Zend Optimizer FAQ answers the question "Why use the Zend Optimizer?" with this statement: "The standard Zend run-time compiler used by PHP is indeed extremely fast, generating code that is usually 2 to 10 times faster. But an application that uses the Zend Optimizer typically executes another 40% to 100% faster."
Read the results of the load test HERE.