what are your goals.
numbers on the term lab - and being able to show out real fancy like at a car show demo area
are you wanting to enjoy the sounds of your music that are pleasing to you at medium to moderate levels - and have the ability to crank up to demo here and there but mostly its built for your skilled ears to hear the amazing in music - not just pure spl loud
i say this because i just did a c pillar 4th in a burb. yes it filters out mechanical noise and other bits that a flat wall is not capable of but
the air space in the cabbin that is left once you build will be either your sonic enjoyment or your frustration in trying to score on the meter.
b pillar builds take away so much air space from the preasurized areas of the cabbin - its almost impossible to not float shirts in the windows and hair trick on b pillar builds - but same build just further back in c pillar has so much more cubic air space in the cabbin of the viechle to preasurize its much harder to score big numbers on the tl and or also hair trick / float shirts in open windows... bla bla bla - but the sound from the c pillar build will most likely be more enjoyable at reasonable listning levels to the users inside the viechle as there is still sub imaging and some space for the sound waves to travel before they hit you.
either way - your roof will be your biggest enemy. flex and ugly noise will need to be dealt with before building the wall - as once the wall is in - your stuck with whatevers up there and cant get to it.