I've wondered the same thing. Anyone have some sound clips of either?
I am a huge Magnaflow fan, but their stuff is getting a bit heavy on pricing. It's definitely nice and the 4" race mufflers on my True 10.5 car sounded unbelieveable, even the 3" on my old 9-sec. Trans Am sounded nice.... but haven't heard any on the GT500's.
reason i ask is because there are plenty of videos and opinions on the magnaflow magnapacks 3" exhaust for the gt500 but i havent heard of very many with the borla 3".