I'd only throw on a set of header if you plan on building a N/A monster or supercharging it in the future.
I doesn't really increase the performance, a little bit in the mid and top and a slight loss in the low end.
It made the BRM sound much
different, kinda lost its smooth deep tone. I plan on getting another resonator welded in before the main resonator, Vibrant Ultra Quiet, a short wide oval res that apparently makes quite the difference.
With the stock manifold, it is one of the best sounding exhausts out there for the S chassis.