Concerning big bore throttle bodies:
Keep in mind that the intake system is exactly that, a system. Upgrading just one component isn't going to make much of a difference. In fact, upgrading all but one component isn't going to make much difference due to bottlenecks. In order to get the most benefit out of a big bore throttle body, you must upgrade it, the intake, the intake manifold, and (preferably) port and polish the head. That way, you can flow more air through the entire system. What good is a bored out throttle body if the intake manifold can't flow that much air?
Also- the ratio of the diameter of your intake piping to that of the area of the throttle body plate isn't a mistake. This ratio is important because it creates the right amount of pressure on the intake plate from charge air. If the intake tube is too large, no pressure is generated. If it is too small, you can't flow enough air. Ever wonder why the AEM cold air intake (2.5") produces more power than the Injen cold air intake (3")? Now you know.
If you still want to get one, I'd look at the JDM ITR, Erick's racing (
www.modacar.com), or the Spoon (
www.inlinefour.com -my favorite online shop). Add that to the Injen 3" cold air intake and a Skunk2 intake manifold, and you'll have an extra 10-15 to the wheels over stock.