Sound is subjective on the I-6. Some like it, a lot don't and there is no way to make it (EVER) sound like a healthy V-8 -- just not in the cards -- so take that into consideration. Our I-6 is going to sound "ricer" for the most part, and that's 'cause the design has more in common with ricer cars than with small block Chevys.
Power increases are negligable. If you have a lot of money to play with, or your stock system is due for change, go ahead, you'll gain a couple hp -- but not really worth the cost for a decent system. Cobbling together a "big" system has proven to hurt instead of help performance, as many here on the board can attest.
Best bang for the buck (costs under $150) is the PCM for Less tune. Makes the most difference for the lowest $$$. :thumbsup: Couple that with an exhaust and CAI, and you will gain a few ponies and a lot of drivablilty, but it still isn't going to (EVER) be a tire-roasting race truck.