custom exhaust

[BRSTYLE240SX]

i like torque! I want torque! what would the affects (on torque). Different setups, both cat-back exhausts have the following in common!
- goes straight, no bends like the stock
- beggins with a hi-flow cat
- ends with a straight muffler, some racing kinda muffler, you know, with the tip (single) being over 3 inches, maybe 4 inches!??

Here are the different "middle sections of the setups"

1- straight 2 1/4? straight 2/ 1/2? straight 2 3/4? affects on torque of each of those? Take into consideration the other characteriscs i mentioned above.

2- going 2 1/4 inches, and it would then increase to 2 1/2 or 2 3/4!<img src="http://www.zilvia.net/f/iB_html/non-cgi/emoticons/confused.gif" border="0" valign="absmiddle" alt='???'> What would that do to torque? and hp? Take into consideration the other characteriscs i mentioned above.

3- And the other way around, begginning with 2 3/4 or 2 1/2 and halfway it would decrease to 2 1/4. What would that do to torque? and hp? Take into consideration the other characteriscs i mentioned above.

Thank you, I'm getting a custom exhaust this month, and would like to know the answer to this so i can make the right choice!