custom exhaust question

[Justin99GST]

I have a friend that works at an exhaust shop and can build me any exhaust of my choice. I'm thinking about a 3" cause i have heard it tends to be a bit deeper than the 2.5", should i just have him do a cat-back or a full turbo back. If turbo back how should he do the DP? Start at 2.5" until the flex pipe then step up to 3" or just 3" all the way. Also he told me to pick the muffler of my choice and I think I'm gonna go with hks hi-power or a titanium greddy muffler. Any comments or suggestions would be helpful, thanks.

 

[EclipseTrbo420A]

I would do a 3 inch turbo back. He can get reference from a picture of an ebay downpipe.