Mandrel bending versus regular

Putting a 3" exhaust on a 318 170hp engine isn't going to care if it's mandrel or compression bent. IMO, a general you'll gain x%, one versus, the other isn't really accurate if the tube isn't sized correctly at the start. Heck that 318 might just run better with a compression bent set up!

So the question really is dependent on application.

All things considered, mandrel is better because of restriction issues.