2 1/4" would be fine. Just keep restrictions to a minimum. I read one of those lengthy articles posted on here a couple months ago. What it comes down to is, bigger isn't always better, smaller is worse, consistency is best. You want good flow by volume, but also to keep exhaust velocity up. I'm gonna go 2 1/2", and that's on the large side. You want smooth bends and no hang ups. Whatever size pipe you run, take that exact size right out the tailpipe.
This means: Don't knock the crap out of your cat, it will not help. If you need more flow, get a bigger converter with the right inlet and outlet. The turbulence in the gutted cat drops exhaust speed. Run 2 1/4" from beginning to your muffler. The exhaust velocity will help "pull" spent exhaust gas from your cylinder, making for a better intake charge. Bigger pipe will kill the velocity.
Oh yeah, I like stainless too, my exhaust rusts quickly from short trips to work.