Unless you're just going to 5" cuz of the noise or cuz it looks "so cool", don't bother unless you're running big HP, just change the muffler to a 4" straight through free flowing one from Nelson or Donaldson.
Put the money you saved towards something that will actually get you some hp improvements.

 

True to that! Just delete the muffler/cat and run a 6"x24" magnaflow tip, and there's the 5" tb sound maybe not so much turbo sound tho.

 

In terms of performance, I think it is like someone asking if a fire hose nozzle is better than a garden hose hozzle. If it is going on to a fire hose..heck ya... there is a huge difference...if it is a garden hose...no difference. It is the same with a motor,. If you are running big boost at high RPM then the 5" work great. On a stocker the 4" is more than enough.