Code P0430 and Engine Stumbles When Accelerating

[X5Cat]

The wife's 2009 X5 3.0i is giving the P0430 code. It starts and idles fine but when you accelerate moderately to hard, or when there is a power demand like going uphill, it "stumbles", jerks and shakes until you back off of the accelerator. Anyone been down this road before with the E70? Can someone tell me how many O2 sensors it has, and where they are located? Also, where #1 cylinder is on these engines, so that i can identify Bank 2? I am thinking to start with the Bank 2 downstream, since I read that the P0430 code is for the Bank 2 sensor. I thought upstream sensors were much more likely to go out before downstream ones. But, I read somewhere that a CAT efficiency code like the P0430 points more toward a downstream sensor. A little extra brain power from you guys would be appreciated. Thanks!