Server Upgrade - Garbage Collection with a new CPU

The site has recently had an CPU upgrade from a AMD Sempron LE-1250 to a AMD CPU Athlon 64 x2 7850 Black Edition Dual Core. So far so good, with quicker serving time and quicker garbage collection. There's still a fair amount of testing to do to optimize the JVM garbage colection with the new CPU (link). It's an complicated area with a ton of tweaking you can do - options that are currently being looked at - -XX:+UseParallelGC -XX:ParallelGCThreads -Xincgc -XX:+UseConcMarkSweepGC -XX:ParallelGCThreads=2.

Update: It seems -XX:+UseParallelGC is used as default for server-class machines - http://download.oracle.com/javase/1.5.0/docs/guide/vm/gc-ergonomics.html