I had the whole package done; header, hi-flow cat, midpipe and cat-back.
First impression, first gear is very smooth, no jerking. Second impression, it pulls and pulls and pulls. Actually, it was kinda of embarrassing, to hit the fuel cutoff (several times) @ 6200RPM. Nomally, you can tell when you are 'out of gear', but because it now pulls all the way to redline, you can't tell (for the first few days anyway).
I would strongly recommend this to anyone. And I haven't even mentioned the awesome sound it makes.