X & H pipe vs straight dual exhaust

Thanks for all the feedback so far. There have been many different thoughts on this subject and in the end it looks as though I may be just as good to use a straight dual exhaust system. I plan on using the flowmaster 40 series mufflers but the jury is still out on an X or H pipe or just go straight thru exhaust. I was happy to see a 15 HP gain but then others say there is no gain. If its only a noise reduction, not sure if its worth the cost.
Rodney