[CentOS] Upgrade 4.7 > 5.3 poorer 'performance'

Hi

During a test upgrade of a number of hosts in a pool i have found that 
exactly the same JVM based app runs more efficiently on the 4.7 systems 
than it does on the 5.3 on identical hardware.

Specifically the apps seems to exhibit about 10% more 'load' on the 
CPU's for the same workload - before i start digging deep has anyone 
seen anything similar ?

thanks