you could also run a aftermarket midpipe with stock muffler. It deletes second cat and resonator. I have one new for sale actually. The axlebacks for the gt are more expensive than axlebacks for the sport as usually they are y split, and you will get a much more agressive sound with a straight midpipe and stock muffler. But axlebacks if you have the funds offer a good sound as well, cuts weight, and you do get some gurgles. You also get nice options visually to look at vs the stock muffler( burnt tips, carbon, etc.) i think the midpipe may give you a bit more on the HP side but not much. I ran both (when i got midpipe but took off as soon as a put it on. tested.) but was way to loud straight piped all the way back from downpipe. so I just run axleback now as i got rid of my stock muffler.
If you want some website ideas just look around the forum. I use:
Pierce motorsports US
n75 motorsports CAN