Speaking from experience - as I had a 4.2 and decided to fit OEM MC Corsa back box on it 6months later to palliate for the inaudible soundtrack of the 4.2 - I can tell you the car sounded just like the 4.7 MC (and slightly better than regular 4.7S). However, not having a valve system, the loud sound was always on - which wasn’t a problem for me, although could be annoying for a daily driver.
To be honest, I even had bought a valve kit which I never fitted.
What the upgraded exhaust didnt do though, was make up for the actual performance gap to the 4.7... but for everything else, there’s MasterCard ! No wait, what??