Actually a high flow catted DP will help a lot due to the fact you are replacing TWO stock cats with one high flow unit. You will get performance and sound bennefits. As to how noticable they will be. HP and torque will be maybe +10 to +15 with slightly quicker turbo spool. But with the AP or Tune that this would then allow for, gains would be significant. Sound bennifits probably only noticable to you.im looking to keep my exhaust pretty much stock but i've been looking into hi-flow catted downpipes recently. I was wondering if swapping this into my exhaust system alone will have noticeable benefits ex. power gain and a slightly better sound.