I do wonder if this will become a hot topic again. After seeing the same thing mentioned for at least 2 generations (read: the past 13 years), I think it is safe to say that power does not hold any sway when it comes to selling consoles. Yes, some might buy into the 'sharper images' thing but in all, if you really need to compare the size of your whatever, you go PC baby :).
I am certain they will end up comparable with a slight advantage for Microsoft, as is always the case. As long as neither of them fucks up before the release, Sony will sell most.