You wont lose horsepower at all, you just wont feel the true gains until you get better heads and a cam. I have a similar setup up as you, actually the exact same, a Cobra Intake,Mac 70mm,BBK CAI, and the exhaust is the same. I put the 70mm TB on because i plan on big mods in the future, but 65mm would be better for you if you dont plan on modifying your engine. I felt a noticebale difference when botling up the Cobra Intake, especially up high in the RPM's. With the TB and the Intake id say a good 20HP, you should feel it. You may actually seem slower off the line but should definetly feel the difference up high