Not only do you need to deal with the power and torque comparison between cars, you need to consider the relative weights. I have no idea what a Camarobird weighs, but I bet it's more than a Mustang since they look like such hogs.
The Spintech side exhaust is cheaper because it doesn't include side skirts. The Borla kit does (dunno about Steeda). The Spintech exits just sit under your existing rocker covers. Up to you whether that's enough clearance to the road or not.