IMO the mani is the most important part of the exhaust system. I think most of us at some point WILL remove the cat but of course we need to be able to have the cat there for the MOT, if the manifold was to be too long that it needed the cat removing, what would happen when you need to put a cat in for the MOT? You'd have to chop up some of the mani to get the cat in! (Unless you move the cat further down the pipe). Also some of us don't like loud exhausts. And another thing that Joz hasn't mentioned, he said on his old exhaust system he first had no silencers, and there was a loss in performance until he had a mid section put in.