Changing the exhaust will not create or reduce power, it will simply shift the peak of the power band. Making the shift can affect fuel economy. The factory exhaust is setup to balance power against fuel economy.
As one exhaust pulse moves down the pipe is creates a vacuum behind it that helps to pull the next pulse along. This is called "scavenging". If your pipes are too small they become restrictive and this doesn't happen because you create a backlog, so the engine has to work to push the exhaust out. If your pipes are too big you also loose this effect because there isn't enough exhaust being produced to create the scavenging effect and the engine has to work to push the exhaust out.
Also, the cats are designed to help in this method of operation. When operating properly they help contribute to proper flow through the system.
If you increase your pipe size between 1/2 and 1 inch after the cats you may gain a little more low end, but you will lose something at the top. If it's a bit more pep on take off that you are after I would suggest upping the pipe size about 1/2 and inch after the cats and putting in a glass-pack muffler. Traditional mufflers, with their baffles, are the biggest actual restriction in a factory exhaust.
I am not trying to discourage you from anything, but it sounds to me, from reading a bunch of your posts, that you are after cheap performance. There is no such thing. If you want real power gains it is gonna cost you.