With the stock headers your turbo will spool up quicker, most kits are designed for stock headers which is nice. If u use the stock headers get rid of the cats, just my .04$
LT headers work nicely with SCs
SOLD-ZL1 M6:BTR,LTs,IDs,ATI,RotoF, AFCO. 10.84@129
SOLD-2011 SS M6: Blower, Cam, LTs, Alky.