exhaust

I am going from sinlge exhaust to a T.O.G. (the other guys) headers, to a undecided downpipe, then a SLP "power-flow" cat-back. Should i run a catted downpipe or would i see more results from a off road catless one? remember i am not SCed. I do not have a cold air intake yet, anyone know where i can get one for an '06?