I'm a bit of a johnny-come-lately for this thread, considering bowl scenarios is actually one of my obsessions (just ask my wife, she rolls her eyes at the myriad excel spreadsheets that start popping up on the desktop around this time of the season), but it looks like you missed a few possibilites, rasta.
Of the 8 remaining possible outcomes to affect bowl positioning, 6 of them look strongly like your assertion is correct, that it'll be either USC, Cal or Oregon State (and actually, Oregon State is only really a possibility in one instance - Oregon, USC and Cal wins - but even then, that results in a 4-way tie for second between USC, Cal, Stanford and Oregon State (and I've listed those teams in the order I think they'll go to bowls), and who knows for sure. It's everybody's assumption that the Beavers are a smaller draw than the other schools, so yes, they'd likely be last pick of the ties.
There are 2 scenarios that could put us against Arizona again, though. If Arizona and Cal win, we may just see Arizona in Vegas (ugh).
Reason I say this:
-if Oregon State wins, there'll be a 3-way tie for 3rd between Stanford, Cal and Arizona. Assuming the Sun Bowl would want the bigger Stanford or Cal name, and Emerald takes the other, that'd leave us with Arizona.
-if Oregon wins, there'll be a 4 way tie between Cal, Stanford, Oregon State and Arizona. In this case, WHO KNOWS who the Holiday and Sun Bowls will take. Reason being, in MY opinion, of the 4, Cal and Stanford are the biggest draws, which would make one think that they'd go 2 and 3 (which would annoy Emerald to all getout because they'd get no NorCal home team), but who knows which one of the leftovers (Oregon State and Arizona) the Emerald would take, and which they'd leave Vegas with. If I were to guess here, I'd say the Emerald would take Oregon State, as the draw would be about the same, and Oregon State is closer. That'd again leave us with Arizona.
Okay /geek. Thanks for humoring me. ;)