The beauty of the Corsa system is by design. The inherenty designed (Helmholtz) resonator section cancels certain resonant (sound) frequencies and mitigates others as well -
without impeding the flow of the exhaust gasses. IOW, the Corsa IS essentially the same as removing the stock resonator and installing straight pipe in its place. So, there wouldn't be any practical (if any) increase in performance by swapping straight pipes for the Corsa resonator section.
As for the X pipe, specific HP improvements in performance depends on what else comprises the exhaust system, e.g., w/ or w/o headers, mufflers used, etc. But, specific quantities aside, the improvements experienced by many before and after users is "all good": up to 25 rwhp is commonly claimed. (YMMV). I have one (from Stainless Works). My fully ported (except for throttle body) motor with LT (SW) headers, 3" exhausts and somewhat restrictive mufflers makes 432 rwhp (before last improvements). How much is due to the X-pipe? I dunno. But, it's part of the package, and I "think" it helps...so it does!
