hm.. for your header question...
4-2-1 header for torque...4-1 header for midrange-highend performance.

basically a track/street question. (racing from stoplight to stoplight, or from 45mph+ hehe)

i have an apex'i world cat back exhaust... nice deep sound, and produced a nice gain. i'd recommend greddy evo though..

i have dc 421 ceramic headers, and they are just dandy :-P