SerialGC outperforms ParallelGC on a server class machine for a Tomcat/Xythos/webdav application

This is Tomcat test with a Xythos webdav application running in a "one socket, quad-core, 8 virtual CPU" SPARC-VII zone. 50 users, uploading 3 different file sizes (100K, 512K, 1M) but the same file every time. Its a very simple load (though its not trivial to recreate the environment).

Time in seconds for upload: (100kb / 512kb / 1024kb)
  2.410 / 3.036 / 4.248 with PS Scavenge & PS MarkSweep
  1.774 / 2.386 / 3.488 with PS Scavenge & PS MarkSweep & Ergonomics Disabled
  1.481 / 2.090 / 3.139 with SerialGC