Landshart, speak for yourself. (:
I want to come out with one that I will have on my car and would recommend to anyone.
Your long replacement downpipes such as COBB and Perrin replace 2 portions of you stock exhaust, the downpipe and midpipe, thus eliminating 2 stock cats.
Your shorty downpipe replaces the stock downpipe portion of the exhaust and eliminates 1 cat. Here you retain your midpipe and one of the cats. So theoretically you could say that you have created a long downpipe with 1 stock cat at about HALF or less than half of the price.