I have Option Racing flex-back exhaust on my sedan. I love it, it's made of great steel, and sounds really good. I don't know about the header. I originally had an FSwerks 4-to-1 on mine with my OR flex-back. It sounded angry lol. But now I have my factory mani/cat on it, and it sounds amazing. And it's 50-state legal still.
Best bet is to go with the SVT header conversion. But if you can't afford it, just throw a nice flex-back on it, it'll definitely sound cool, if not free up a half a pony somewhere.