The hard part about guessing here is that this generation has more potential to last longer than the last gen. Sure the 360 has a sizable lead now, but this race will end up more like a marathon if sony stays true to its 10 year lifecycle.
That said, I think that if the 360 gets a 8 mil lead before the next Ps3 price cut, it will have 2nd place locked up.
::editted::