I have done the cat and muffler delete pipes. Absolutely love it. Very happy with the performance, sound and cost. About 70 bucks. I have had this set up for about 90,000 miles. Very happy.
Also with living in California the cat delete pipe super easy and convenient.
Don't gut you catalytic converter. Just get the delete pipe.
If you have to deal with a smog program then you are going to need to keep the cat in the exhaust. You do not need the muffler since it is not a emissions device. But the down pipe and cat must remain stock, after the cat converter you can do whatever you wish. But no 4" down pipe or any changes from the cat to the engine.
I can assure you though the open can of the cat smoothes out the exhaust note a ton. I ran my truck with straight pipe all the way back and it was raspy as hell. There was a drone in the exhaust, my old truck had a empty cat and sounded much better than my straight pipe system. So I took the cat from this truck and knocked out the honeycomb and welded 4" pipes to it and placed in the stock spot.
As soon as it was installed the exhaust drone was gone. Strange that a open body has that affect on the exhaust sound but I assure you that it does.
If you want a loud growl out of your truck straight pipe it all the way. If you want to keep it a bit smoother and quieter put the cat body back in.
As far as power gains without the cat you won't get any. The one gain you will get from removing the cat is 100* lower EGT. Mileage will also be the same, the cat does not change the power or mileage. But it does change the sound of the exhaust for sure.
I also installed a Corsa muffler on my truck to tone it down a bit more. It's a straight through design and uses new technology on sound waves. Pretty cool muffler really all stainless steel too btw no packing of any sort.
Good Luck on your truck..............