catalytic fail

[chongasm]

So my cat is going out. Loaned a tool from autozone and came up with a P0420 code reading. I looked around some websites and found that there were usually two types being sold at considerably different prices.

One is for sale in all 50 states and the other is not sold in California. The 50 state legal looks OEM.

Does anyone know anything about the other one?
It looks like this:

http://www.bavauto.com/lview.asp?imgfile=assets/imglib500/bmw1475.jpg
http://www.bavauto.com/lview.asp?imgfile=assets/imglib500/bmw1475.jpg

Is there any difference in performance with this?

Edit: Did a little searching, and read up on what others had to say. I have came to the conclusion that either my cat is going bad or my o2 sensor needs replacement. If it helps narrow down the results any, I have some smoke coming out the exhaust. I just replaced my valve cover gasket so I know oil isn't running down the plugs.

Any help would be greatly appreciated.