I came across the same question when I looked at it before. I wonder if the same exhaust for the Canadian 323i would be suitable..
The potential issue with putting a big exhaust on a smaller engine is there may be a drop in the low / mid-range power. It is related to the lower velocity of exhaust gasses in larger diameter tubing. I think the centre section of the Performance exhaust is a 2.25" pipe, so I don't know for sure if it is too big or not. I got the idea that maybe it would be better to delete the secondry cats and change the muffler, keeping the stock centre section of the exhaust. I'd like to get an informed opinion before making changes because I am only interested in doing it to get a performance gain.