Here is a 360/300hp exhaust dyno test. As mentioned, the more HP, the more headers will help. While the individul differences aren't big, those improvements are throughout the RPM range which will make an obvious difference.
I've been using TTI's for years and they have many advantages besides the HP and torque. Easier installation, plenty of ground clearance, thicker metal, etc.
The dyno charts are in the last pic.
Exhaust on a Mopar 300hp Crate Engine - Tech Articles - Mopar Muscle Magazine