a cat back and intake will give you some noise and good looks, if your looking for more power there is nothing too helpful for the soul yet, you wont notice much difference if any in power with these two modifications, now if you removed the cats and do a full exhaust with id say 2'' piping with the intake you may feel a little difference, im taking my cats out more than likely, doing that should give it a little more pep in the mid range, which i have noticed is a little week, off the line i can keep up with my buddys 2008 SI, but after 30 or so mph i loose a lot of power but get it back around 50mph