Yea, thats a good way of putting it

 

Some people believe a certain amount of backpressure can increase low-end torque and a lack of backpressure will definately increase HP. If you can live with the noise, then go for it...but around here, in NY, the cops would be all over you in the loud *** old car. Inspection?

 

Again, backpressure does NOT increase torque anywhere, what does is velocity, which aids scavaging. Small pipes have higher backpressure, but higher velocity. The tradeoff comes as the flow increases. Low RPM's the engine doen't flow as much as at high RPM's, so a small pipe that has high velocities at low RPMs will be overwhelmed with backpressure at high RPMs. The opposite extreme is also true, low High RPM backpressure often leads to poor velocity in low RPM's.

So obviously there is some tradeoffs when puttng together an exhaust system.... especially when noise is an issue.

As I see it mufflers come with two of the following qualities:
Freeflowing (low backpressure)
Quiet
Cheap

there are good mufflers (rare i'd say) than provide performance with desent muffling.