I believe that is what IBM published, yes (though I've seen conflicting information about the 970 at 1.8GHz... 42W. Where are you pulling 51W from?), but as was recently talked about in an AnandTech article, IBM seems to list power consumption at "typical" levels and others use "maximum." They also mention that even some of the speed adjustments at higher levels have core voltage increases accompanying them, so it may not scale as expected the higher one goes.
As usual, it would seem hard to pull real-world expectations from white paper numbers without a lot of other accompanying examples.
