3" exhaust or 2.25-2.5 y pipe?

[KOMPLICATED]

I was just about to oder my exhaust when i saw the Y pipe. Not exactly sure what it's called, But it splits to where you can have it opened to the atmosphere or closed off onto stock piping. Now would I make more power from that or a 3" cat back. My cat is gutted, and will probably be buying a downpipe at the same time.

 

[L2RTSiAWD]

An exhaust cut-out is what it is. for when you are at the track you can elimiate the rest of the cat-back.