Do I know how how you feel. Totally and completely. It seems we have done a lot of simular up grades in hopes of achieving that awesome deep aggressive growl that comes naturally from our more powerful siblings, the V8. I know that sounds Korney but its true.
Anyway, I spent hours upon hour's at Youtube listening and comparing other V6's exhaust. I finally narrowed it down to two. Borla's "S" type or SLP Loudmouth. I decided on Borla! But somehow I got talked out of it and into Fords Racing True Dual Exhaust. Those had their good and not so good points. The good was at least l now had true dual exhaust and could put anything the GT used, well, so could my pony. And then BORLA came out with ATAK and my dream of my baby pony sounding as good (for a V6) as her V8 sibling came true. But seriously. If you want a great sound. Either Borlas ATAK or SLP Loudmouth. Check them both out and see what you think. What l think sounds cool you may not. What I used to type in was 2007 mustang
V6 Borla exhaust or SLP loudmouth exhaust. There are members here that have amazing sounding exhaust. Good luck!