Still unclear as to what your ETs are. That could be anywhere from low 9s with everything tuned great on a good day, to high tens for whatever reason. I would say, unless you are running mid nines at worst stay with your C4 and spend that money on something else, because it will make for a boring ride. A friend of mine would let me drive his cars at the track and his high 8 sec car with a glide felt slower then his 9 sec car with a C4.