2.5" or 3" catback best for a automatic GST?

[Six97GST]

I have a mostly stock 97 automatic GS-T. I've been told that it would make more sense to get a catback with 2.5" piping as apposed to the 3", since my car is an auto with the stock turbo. Does anyone else agree with this? I would like to upgrade to a bigger turbo some day, but I want to at least get a used TD05 (stock turbo from the 5-speed I believe). Which is the best way to go? Thanks

 

[SOURCE1064]

2.5 is fine untill you go for a big boy turbo. 20G and up I would suggest 3".