I was in a straight piped GXP last fall for a tune (no cat, no res, no mufflers), needed Tylenol at the end, sounded great for the first couple of minutes though.
Run a Magnaflow 12641 in the resonator area and even with straightpipes in back the exhaust tone will still be fairly loud but won't be raspy and you'll have very little to no drone http://www.magnaflow.com/02product/s...=main&id=11455