like some have said, welcome aboard!
to start things off, many companies have seen that on the 6 (we're talking 4cyl for now) there are not gains to be had by increasing pipe size. why spend the extra money (and charge more money in turn) for something that isn't needed? though there is some minor top end to be had, it's in most cases, not worth the cost. as someone already stated, which i really liked, if you aren't racing it's about enjoying the ride. this is what companies (and you) should be focusing on when looking for an exhaust. if you feel you got a gain, that's awesome.....but you didn't. the butt dyno is more important for daily drivers anyhow, so that's what i would stick with unless you plan on really sitting on a dyno with the car.
hope that answered some of the questions for you. and if you have a custom shop that does work for you, you WILL see some gains if you want them to fab up a mid pipe from header to the beginning of the exhaust (keep the cat or go with a highflow) as that is the biggest restriction in the system....making anying bigger after that is post-bottleneck, so just for looks and sound.
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