Go for it!!! There are a few people around here running 3" cat backs around here (including flex pipe) I think it was Tom who posted some time ago about the gains to be had from a 3" flex back and flex pipe. I don't remember what the gains were off the top of my head, but they were noticeable and worth it. If I had the money I would definitely be adding a 3" ORP back, but alas I am mostly broke..
The stock flex pipe is a major pinch point, it was smaller than the tubing on the rest of the SVT exhaust setup.
woot to post #69. I like that number, 69. It's just such a pleasurable number.