I am certainly glad that I did not proceed extensive mods (such as long-tube headers and high-flow cat-back) before deciding to go with the TT Kit - turns out that there are specific implications on the TT kit that either replace or restrict specific upgrades.
For example, I was in the process of selecting new headers and cat-back products when I discovered in this thread
that the AGP Kit would not be compatible with the headers that I initially selected and furthermore, was recommended to stick with the stock exhaust. Basic concept was that even beyond the incompatibility to the base kit, the minimal HP gains from the exhaust are dwarfed by the increases from the TT.
Given that the cost of a good header and cat-back exhaust is close to $2K, that is a bunch of $$$ saved. Even my CAI will be replaced by the twin CAI's in the TT Kit, so lesson learned here is: Establish your upgrade plan early, especially bigger decisions like blower or turbo, which will dictate an entire mod path...