twin exhaust

I'm getting a dual X pipe installed in my car. My question is what would the best diameter exhaust be? I also have plans to port the intake and the heads if that makes any difference. Thanks

I have a twin exhaust on my 1uz conversion. 2x 2.25" (57mm) stainless pipes from headers, right through with 2 silencers per pipe. (I drive alot soI don't like it noisy) Makes awesome sound until you give it enough throttle, then it starts "clapping"/ "clattering". I have a balancing tube about...