Piping Size for Custom Exhaust

Hey guys. This is my first post. I traded in my '06 Civic Si and bought an '11 Toyota Tacoma SR5 V6 4X4 this recently past monday. I have to say I love it so far.
Now I'm already looking to build my own custom exhaust. I was wondering what size piping is best for the 4.0 to exhale through without hurting my low end torque. I want a nice sound but more importantly some better performance. I plan on constructing my exhaust from the cat on back using mandrel bends and plan on doing 1 in and 1 out. Keep in mind I do plan on adding some other mods in the future (intake, headers, and maybe a chip or piggy back) so i want the exhaust to compliment my future modifications. Any help would be appreciated.

 

Stock us 2.25 inner diameter and some kits go up to 3" so I wills say 2.5" all the way through

 

Thanks guys. thats what i'll do then. How are the shorty headers for these trucks? Do you see or feel any real gains with these or are they worthless?

 

I did 2.5 on my custom setup as well..