Yep, you should have said what year car you had from the get go. I MUCH prefer the H-Pipe sound over the X-Pipe on the 4.6L Stangs. Sounds more aggressive IMO.
On the new 5.0L cars, saying that changing the exhaust isn't going to net you any gains is pure ignorance. Going from the stock exhaust to an O/R X-Pipe makes a significant power gain that you can test, feel and SHOW on these cars. It makes, IMHO, getting headers a waste of money on an N/A 5.0L. The X-Pipe is all you need. I'm not sure of the exact figure in gains, but I've seen it before and it definitely passed the HP-$$$ ratio!!