I had that #1 on my car and can tell you from experience that the 4-1 header piece is garbage I threw it away 2 days after I installed it because it started leaking. I did use the downpipe however but did not notice any difference in performance whatsoever. Also depending on the brand of your exhaust the noise level inside the cabin probably will be very very annoying at cruising speeds. I had 5Zigen Cannonball catback and it was really loud, but then I switched to Nismo catback and it became a lot better (both were 3"). From what I heard HKS Hipower and Apexi N1 are relatively quite on KA so would suggest those to you if were to install a header and resonated pipe in place of your cat.
As for #3, my guess is that it will be the loudest one of the three and you might encounter a fitment problem with it.
Performance wise all 3 are in the same neighborhood and will not give you noticeable power just the noise. Save your money and buy name brand because they were designed to increase power except Greddy.hot shot is probably what I would go with and you can find used one on ebay for around that much. My second choice would be DC Sprts.
This is the dino I found that Orion from freshalloy had on his website. Apexi N1 and Apexi cone filter were installed before the header.
http://ka24development.com/fil...t.jpg
Modified by dm-ka at 10:54 PM 8/19/2009