With my truck I was thinking of dueling it out myself with a magnaflow muffler. What is the performance/sound difference between a dual in - dual out muffler and a single in dual out muffler. Also what size pipe should I use? And what size is the stock pipe leaving the cat. converter? What I would like to do is put the muffler on then run to just behind the axle and turn it down. In doing this would there be any noticeable difference between running the pipes side by side and running one on each side of the spare tire?

thanks