You use conflicting GC settings and I don't know what the JVM prefere in this case.
See http://www.oracle.com/technetwork/java/javase/tech/vmoptions-jsp-140102.html for detail on options.
I prefere UseParallelGC (only not Old) or 'UseConcMarkSweep AND CMSIncrementalMode' but the performance depends stron on the application memory footprint :(
So I recommend to not think about optimizing without measure the app, you should drop NewSize option and try to use NewParGC or CMS.
See what happen, you might watch with jstat or VisualVM.
Also I miss the information about the JVM version...