[stanglifemike]

I dont think you need to go with a 3" system unless your planning on going FI soon. The 2.5" is sufficient. As far as the midpipe go, an o/r pipe will give you a little power, either x or h. Axlebacks are strictly for your listening pleasure. Definately listen to the o/r h and x pipes before you buy 1. They sound different on these 3v's than compared to the 2 and 4v's.
Headers will be your biggest hp improvement with your exhaust, I would say expect around 15rwhp from headers, give or take a few