hey, HKS carbon-ti is a really nice sounding good performing exhaust. the only downside i see is that is dips rather low almost like apex'i units ( i dont understand the rational behind dipping so low. granted, the exhaust is going to have a slight dip due to the rear differential, but hks ti and apexi n1 tend to dip more than most others). i am still trying to decide between hks carbon-ti and blitz nurspec exhausts. turboxs has a GREAT exhaust that supposedly (when used in tandem with turboxs dp) produces upwards of 30whp. they both sound very aggressive and intimidating (not sure if that is what you are looking for). as for high flow cats, i cant help you there, i plan to go catless (i feel sorry for any motorcycle driver behind me in traffic ) i live in va but am going to register the car in sc. are you going to go divorced or bellmouth dp?