Oracle Forms 11g JVM tuning

I'm looking at building a Windows 2012 server to run two forms and reports instances. Each instance will handle up to 150 concurrent session of which a maximum of 10% will be active. I'm pretty au fait with building these instances and getting them operational, but one thing that I have no real experience is tuning the JVM generally, particularly with regard to the expected workload and user demands I've outlined.

In a previous instance built to cater for 40 concurrent sessions, the only tuning I applied was setting the WLS_FOMS EXTRA_JAVA_PROPERTIES from -Xms256m -Xmx512m TO -Xms1024m –Xmx1024m