SuperAirborne, you haven't mentioned what type of aircraft you are wanting to make fly faster , and indeed how much faster. Before you consider making drastic changes to the prop, find out just how much faster your model will safely handle. All airframes have a terminal spped, and if you over prop it , then the spectators will see an amazing site as your aircraft shreds itself to peices in midair, while you shudder at the waste of money becoming confette at an enormous speed that the airframe couldn't handle. So i suggest you do more research as to what maximun speed your model can handle.
Besides all that , welcome to the wonderful hobby of model flying
bill