Have a read of this thread. One of the "fleet" which I look after has the exact problem....bit different to yours.... goes like stink throughout the rev range, but at tick over fuels too rich, stuttters and stumbles and throws up the dreaded misfire codes.
I have read loads of unresolved threads on the problem, which in the good old SU Carburettor days would have been rectified in 10 seconds flat, but seems incapable of resolution by the finest brains on the internet, and most definitely "main dealer" finest brains whose final recommendation of the "it could be that so we will replace it approach" is usually "engine replacement"
I will offer a bit of an answer to one of your questions, and I could of course be 100% wrong, O2 Bank1 Sensor 2 would have no effect at all on your misfire. Its downstream of the Cat, and may get its trouble code thrown up as a consequence rather than a cause of the misfire.
So in conclusion I watch this thread with interest, and wish you well, but hopefully more knowledgeable members will be along with more practical advice. I did see a thread which Simon (Mandrake) contributed to recently with a logical method of investigation into such problems, rather than replacing bits which could be the cause at random.
All the best
Neil