Sometime ago, there was performance blog saying that some of the performance stats published on WSO2 ESB are incorrect and flawed. So, WSO2 ESB team has carried out some investigations on these and published the latest performance test results based on their latest release WSO2 ESB 4.8.1.
The latest round of performance testing results published by WSO2: WSO2 ESB Performance Round 7.5
The tests has been conducted against number of leading open source ESB's and it is proven that WSO2 ESB ahead in almost all the scenarios.
You can download the latest WSO2 ESB 4.8.1 at WSO2 Enterprise Service Bus
The user guide and the documentation can be found at WSO2ESB Documentation