You want to tune your JVM and wonder if there are any standard settings that Adobe recommends.
AEM (CQ) does not behave differently than any other Java programs out there when it comes to JVM parameters. There is no default setting. Every application built with AEM has different characteristics. Each could require modification and observation until you find the optimum values for your JVM.
Make sure that you look at the available JVM options from your JVM vendor. For Java sun, it's here: http://java.sun.com/javase/technologies/hotspot/vmoptions.jsp. And on the Internet, there are plenty of articles on tuning JVM; most of which are applicable to any Java program.