Crap... Sorry, I forgot you had the P0420... Have you checked for exhaust leaks before the cat. Fresh air sucking in can also cause an issue.
Yes... The upstream could cause it, but highly unlikely and very indirectly.
The link you provided is for the downstream sensor which would/will be the correct one if everything else checks out. Your original video may also point us to a clogged catalytic converter now that I think about it. xci, what do you think of this?
http://www.youtube.com/watch?v=QiHlU9WNha4&feature=youtu.be
V6 Upstream (Before Cat, On Header/Downpipe):
Click Here, Denso 234-4727
V6 Downstream (On Cat):
Click Here, Denso 234-4621
Ever hear of an IR thermometer, phi?
Basically, the test is that the cat should be at least a 100 degrees hotter at the tail end than the inlet end. Call it an oven of sorts. Basically, drive the car around a while, then get the IR thermometer nice and close to the front of the cat to reduce interference. Do the same thing for the rear. You'll do this on the actual piping as close as it gets to the actual cat.
https://www.youtube.com/watch?v=9VZ5K8n5jj0