Their are whole lot of difference between PS 8.4 and Later but few as follow:

Changes in OID(Object Idetifier) , BPEL,Analytical Tools,Security,Integration Broker.

App Srv and Web Srv Performance

 PSWATCHSRV now detects and terminates processes that remain in

the “idle” state

 Timeout for Processes Unable to Start

 Preload Cache on Boot

 Parallel Start and Stop of Application Server Processes

 Dynamic Recycle Count

Thanks,

Parthiban - Comprobase Inc