Your fine with just a dp and stage 2, practical experience and cobbs own literature suggests that the primary components are the DP and for safety sake the UP that need attention. lots of people ( see cobb's own forum) run stage 2 with stock exhaust components myself included. There is some speculation that increasing the exhaust tube diameter reduces flow rate and as a result the gasses become denser as they cool, etc,etc,etc.... But im not a god like authority on the physical universe. What I can say is that my car hits the "target boost" with stock exhaust components from the DP back without any coaxing or tensioning the wastegate. Somthing to consider which appears to be widely overlooked is that when you shorten the arm and preload the wastegate that initself does not allow it to hold anymore boost there is a point of diminshing returns once the assembly is preloaded. The amount energy the spring can supply does not change because it is preloaded. Its like changing ride height on a bike or car preloading the spring does not increase its rate. I like the quiet stock exhaust and from what I can tell Im not giving up a whole lot with this setup. I believe someone did a back to back test to determine back pressures from various setups, it was a really good post. That would shed some light on how "necessary a full 3in TBE is.