I will be changing out my exhaust in a week or so. I wanted to have a comparison so I made a set up and recorded it while using my cell phone's sound meter. Now I can compare it to my Roush set up.

 

Here is the sound with the Roush oval two stage mufflers with factory resonator after the exhaust has been warmed up

You Tube

 

Generally, an H-pipe sounds better on a GT. It is less raspy and will have a nice rumble. The lethalperformance h-pipe is a nice, non-expensive option

 

^^^^ Thru personal experience, agreed on H-pipes providing deeper/gurgling exhaust tones over X-pipes which are well known for producing raspy/higher pitched exhaust tones...
Therefore, I would never recommend to anyone running a X-pipe exhaust kit without including either retaining the stock catted mid-pipe section or upgrading to high-flow cats which will at the very least, reduce the amount of exhaust tone rasp...

However, I would much prefer sticking with a H-pipe exhaust over an X-pipe kit for GT models, hands down IMHO!