4 to 1 carb rejet

Hey everyone. I've been debating getting a 4 to 1 exhaust system for my kz550 because my pipes now are dull and beginning to rust out. I've read a lot of posts on the forums about it. It seems that some people don't need to rejet while other people do need to rejet. How much of a change if any is usually required in the jetting for a 4 to 1 if the rest of the bike is completely stock? Also does anyone have a recommendation about which exhaust system I should switch it to?
Thanks

I found this if it helps. kzrider.com/media/kunena/attachments/11624/PodInitalJetting.JPG