If I can help:
-XX:+UseConcMarkSweepGC -XX:+CMSIncrementalPacing -XX

arallelGCThreads=4 -XX:+AggressiveOpts -XX:NewRatio=3 -XX:SurvivorRatio=3 -XX:TargetSurvivorRatio=80 -XX:MaxTenuringThreshold=8 -XX:+UseParNewGC -XX:MaxGCPauseMillis=10 -XX:GCPauseIntervalMillis=50 -XX:MaxGCMinorPauseMillis=7 -XX:+ExplicitGCInvokesConcurrent -XX:+UseCMSInitiatingOccupancyOnly -XX:CMSInitiatingOccupancyFraction=60 -XX:+BindGCTaskThreadsToCPUs -Xnoclassgc
Those are the parameters I'm using on the Curse client.
Edit

is ": P" (without space). Change number of threads to the number of cores you have available or want to use.