Mark,
Thanks for checking out my site. To be honest I do miss my old GTS, it was a rock solid car, never let me down and looked great. If I could have kept it along with my new car I would.
Regarding power/torque below 3,000RPM - you've got to be careful when choosing an aftermarket exhaust - get something too big, you'll lose a lot of back pressure and you're low end power/torque is gonna get worse, not better.
as an example, look at this power graph for a Fujitsubo Legalis R exhaust - notice bottom end power and torque are way, way lower for the aftermarket exhaust than the std one...
Their super R shows an improvement, but you're not really gaining much below 3K RPM:
Just saying, choose an aftermarket exhaust carefully and make sure it's specifically designed for an N/A car.
Dave