Oracle Database Discussions

Hello Folks,

we have oracle 10g(10.2.4.0) on linux (64 bit-can use ram > 4gb) with 12 gb ram,total sga size 5gb,pga_target=500m
plan is there increase ram to 16gb(already finalised) and later to 32 gb(likely to be finalised) since suspected
sort area is not enough for application to run long queries,on average about 200 concurrent users online(max-380)
sga_target not enabled due to some limitations in setup,i am more concerned with resizing pga as its reported
sort area is not enough
i refer to some oracle docs and notes ,got some suggestions of using queries for views to pga advice etc
but not clear picture to arrive at any specific rule for sizing pga

v$pga_target_advice for PGA_TARGET_FOR_ESTIMATE 400mb showing ESTD_PGA_CACHE_HIT_PERCENTAGE-52%
also i generated reports of sga usage for month found most of time about 5% sga is shown as free

and in one of doc i found some rule saying pga 20% of sga and sga about 70% of ram(i hope this
is not general rule and depend on application)

Please suggest in scenerio when ram increased to 12gb to 16gb,how much should i increase sga and pga
also in scenerio when ram increased to 16gb to 32gb,how much should i increase sga and pga
also its really benefical to increase sga and pga in this scenerio (system is otherwise stable)

Thanks