I got the hole shot on this thread. I personally know and X-pipe kills high RPM power. 12-1 comp 700+ roller tried open headers 18 inch collectors. 3 inch X and a 3 1/2 H. to 3 1/2 bullit mufflers . The H with mufflers worked the best. Our new Demon will exit the fenders with restrictors as seen in the first picture .
X pipes are for little cam low compression motors that pulse. Big cam motors don't pulse at the rpm where they work. If I had a new mustang or Camaro or any pump gas car I would use an X-pipe. Not on a big High compression cammed up motor