I think it's extremely likely both MS and Sony sell out through the holiday season with the early lead going to who ever can manufacture and distribute more effectively.
As the supply problems start to lift it will be about the games, the exclusives on both platforms and how the overall experience of playing the multiplatform games on the platforms compares. Some of that will be driven by graphics, some by online services, some by what peripherals are in the box.
The second Xmas will give a good indication of who made the right tradeoffs unless someone really drops the ball.
I'm more interested in what MS emphasizes at the reveal and the public reaction to it, than I am seeing more beta next gen footage. I think it will tell us a lot about what MS thinks is important and how they plan to market, the public reaction will be just as interesting. At this point though even if the reaction is poor MS still has E3 to recover.
pretty good assumptions I would say