Parts for my 2003 G35 infiniti to add nice HP gains?

I have a 2004 manual G coupe. You should start with a Stillen dual path catback exhaust. It adds the most power out of any other exhaust for the car. The best thing is that it sounds like stock, but louder, no farty exhaust like the other companies. It was also very easy to install. And Stillen race pipes or hi flow cats would give you about 10 horses. I wanted to get the hi flow cats, but they were over 100 bucks more. And get Stillen headers for about 12 more horses,but that is not an easy job, you need a lift and all that stuff. That is all the upgrades i have, excluding the CAI. You could also get Unorthodox Racing underdrive pulleys, which i plan on buying soon, but i don't think i will be able to install those by myself.