Is going w/ a full cat system really worth the extra $200+ as far as performance? A sport muffler will give about 3-5 hp gain which is about equal to a full cat system if I am correct (unless you are Stillen and somehow gain 10-15 w/ a muffler.... )? I have heard that a full cat exhaust system is only a must if one has heavy mods, is this true? Right now I'm running an HKS air intake and HS headers, will a Stillen sport muffler (or any other brand) suffice? Is the extra $200 worth it?