I'm running a header straight back to my 40 series Flowmaster with 2.5" tubing on my 22re. I gained A LOT of power but I think if i did it agian I'd do a 2.25" pipe. I ran 2" and it wasn't enough differance but once I went to a 2.5 I gained a lot of bottom end. There are A lot of guys around where I live that run without cats and don't have a problem at all sound wise. Just make sure put a good muffler on it. I wouldn't want to straight pipe it because its WAY to loud. I ran that way for a while and it just was annoying. I don't know how it'd affect the power on a 3.0 but I don't see it being a bad thing at all, my guess is that you'd really notice the power differance.
