The PSAPPSRV is responsible for the majority of the work on the application server.  It is just as important to start enough PSAPPSRVs as it is to not start too many.  By default, each PSAPPSRV has it’s own Cache folder (unless you enabled shared cache).  For example, if you start 10 PSAPPSRV processes and you only have 5-6 users, it will take a very long time to build the cache for all 10 PSAPPSRV processes.  On the other hand, if you have 5 users and 2 PSAPPSRV processes, the cache should get built up pretty quickly and 2 PSAPPSRVs should be able to handle the number of requests coming in from 5 users.