If your going to be seriouse about it, dont mess around, and get a curtis sparks x6 exhaust. It is freaking amazing when combinded with the Sparks 440 kit. If only I had his cam too. maybe soon. Well see. Reallly loud though, mine idles at 100db and is 103-104 at 4000rpm Other than that, I would highly recomend the WB E-series w/ head pipe. This is the original series they made and it does produce the most performance gains out of the big name brands out there.
Here ares some pics of mine some old some new, you will see both pipes in these pics so yes, I know whats going on...
good luck