I have an E46 2002 BMWi. I have just upgraded to an AEM Short Ram intake. It appears to be a good upgrade but I am concerned about the exhaust being too restrictive now. I was looking at a Borla Catback system but am wondering if there would be a performance decrease going to y split to a single 2.5inch and then into a resonatoer chamber then twin exhaust. What do I want to be wary of. Any Advice?