The HP/TQ differences between an H or X pipe a neglegible on a street car. Let the sound you prefer dictate that choice. There is great a thread in the 2011+ section on svtperformance.com with real dyno numbers comparing the 2 that you should look up.

What you should be more concerned about is the Boss intake. You will give up some mid-range TQ but gain a shitload of horses up top. If you aren't really racing your car you might not want it.

Here's my thread on mine...

http://www.highperformancestangs.com...stall-and-dyno