does a larger exhaust diameter reduce cat effectiveness?
 

On my 87 T2 I have the racing beat turbo back exhaust, which is 3" all the way and has a presilencer instead of a cat.

Massachusetts law has screwed me into getting an exhaust that fits their emissions guidelines. (ie I'm not a fast and furious insider and I can't find a place that'll hook me up with an inspection sticker.)

To spend the least amount of money possible, I'm considering buying the " Bönez Performance Converter (Blank)" from rotary performance, with a 3" pipe on it:

http://www.rx7.com/store/rx7/fcexhaust.html

...I'm considering taking that to a shop and having flanges welded on, and replacing my presilencer with it.

Now, my question: is having a 3" exhaust on the rest of the system going to lower the effectiveness of the catalytic converter? (No, I don't see why it would, since the gas will constrict at the cat the same as it would otherwise, but I always leave open the possibility that there's something I'm overlooking.)