RPG calling JAVA performance

Hi!

I'm trying to improve the performance
of a RPG programm that call Jakarta POI java classes to
generate an excel file!

I've already used OPTIMIZE(40) in CRTJVAPGM for POI-2.5.0.jar,
but i have not seen some significative result,
and after about 10000 rows written in excel work file, the performance
are lower.
Thanks in advance!
Regards 

Vincenzo!

P.S.:
I've tried using environment variable! as follows :

ADDENVVAR  ENVVAR(CLASSPATH)
VALUE('/JAVA/lib/POI-2.5.0.jar:/QIBM/ProdData/Java400/jt400ntv.jar')            
                    
ADDENVVAR  ENVVAR(QIBM_MULTI_THREADED) VALUE(Y)                         
ADDENVVAR  ENVVAR(JAVA_COMPILER) VALUE(jitc_de)                         
ADDENVVAR  ENVVAR(QIBM_RPG_JAVA_PROPERTIES)
VALUE('-Xms512M;-Xms99M;-Djava.version=1.3;-Dos400.stderr=file:/JAVA/lib/temp.out;-Djava.compiler=jitc_de;')