Ok... now that I moved it...
Isnt it skunk2 cat-back has a 2.5 inch piping? If that's the case then you are fine. If you plan to "fully" build your motor for boost, then yeah, go 3 inch. I'm speaking of complete build up which involves anything that will push your motor's stock hp 3 times more. It's insignificant for low boost. The only thing I would recommend for any turbo set-up, low boost or high boost, is to get a high flow cat. It will make your turbo minimize lag. Just be careful, some OBD2 cars will trip a CEL with a secondary O2 code. But it can be dealt with by either using an O2 simulator on the secondary or swap your ECU to OBD1.
If you want a decent turbo kit, get with Hondaman-iac for prices. Otherwise go to
www.homemadeturbo.com/forum to build your own. Review the tech articles on my site and search in the turbo forum. you will be suprised on how many times I've answered questions like yours. Use the turbo forum as a tool.....