Do the Akrapovic headers have a CAT? I'm guessing no, because they're for "racing". So maybe, just gut the stock CAT (or have the right pipe welded in place) and add a power commander. Because the PC5 eliminates the O2 sensor anyway, right? So there's no need for the CAT. I'd like to see that dyno chart compared to the chart of the full Akrapovic exhaust!