I have a set of like new B&B PRT's that many people say are the best sounding exhuast for a C5
they sound incredible without being really obnoxious unless you want to.
They also flow better and B&B say they are good for around 11 extra HP and 14 extra torque.
they are polished stainless steel with the 4.5 inch oval tips, pic installed below
mileadge is irrelevent on these units as they are stainless steel inside and out and not made like regular mufflers, they work with physics in a way that bypasses the muffler to become like straight pipes WITHOUT internal moving parts...very cool engineering actually
here is a link to their website, scroll down to the "Purge Resonance Technology for your C5 "section
these units run over $1,100 new are these are in nearly new condition...will sell outright for $600 plus shipping, you save $500...
can negotiate a little