Well, here's 360's leaked specs from over a year before launch
That has always been my main reason why I think they won't change anything significant from the leaked specs.
This thing has been set in stone for probably a year. These specs is what you are going to get. Maybe a small clock tweak, but nothing significant. Nothing that would overlap a 600GFLOP difference. (This would require a significant higher clock, higher clock means not just more power, but relatively more power, you are getting into a world of hurt when it comes to cooling (for a device that is set in your livingroom)).
In the end, Durango will have its advantages, be it power, size, price, software. That said I would love MS to target PS4 specs