I would describe it as a shift in the torque curve with minimal gains. The narrower OEM tube gives better charge air flow at lower engine speeds, but is a little restrictive at higher engine speeds. With the NM tube the lower engine speed response is delayed a little, but now there are better flow characteristics at higher engine speeds, especially 4500rpm+. It is a trade off depending how you want the car to behave. Bigger does not always mean better.
The best charge air tube to modify is the "hot side" tube. Guaranteed gains in power/torque by getting rid of that stupid silencer.
