I hope you would be interested and find following information helpful.
http://wso2.org/library/articles/2013/01/esb-performance-65
http://techfeast-hiranya.blogspot.com/2013/02/how-worlds-fastest-esb-was-made.html
http://techfeast-hiranya.blogspot.com/2012/09/busting-synapse-and-wso2-esb-myths.html