After trying the usefull "Launch Naiad" batch mode, here a basic simulation to see the difference between to launch a sim with Graphical User Interface and with command line.
In this test NOGUI is faster than default simulation (GUI) : 26%
Post : http://adrienrollet.com/2012/05/03/accelerez-vos-simulations-avec-realflow
Realflow 2012 - Hybrido
Sim: 1 million particles
CPU : Quad Q6700 3GHz