So I got a 84 z28 LG4 engine 5 speed and I got stock headers, y pipe, and after my cat there is a 3" tubing which was a replacement for the stock 2.5" piping it originally had.

My question is that I am thinking of replacing my cat with a high flow cat and my y pipe as well because it has several cracks in it and i am getting a exhaust leak, but if I dot replace my cat with a high flow cat and increase everything from the y pipe down to a 3" pipe will there be some type of noticeable power difference or just I just keep it at 2.5"/??thanks!