Its becoming clear what AMD did with the 290x. They upped the clocks and volts more than they normally would do with newly released cards... just to beat the 780 and get into Titan territory. If they applied the same overhead room as with the 7950/7970, it would've been a rather underwhelming card.
Normally AMD puts out a much more efficient product all around. But I think it is great that they did this.....waiting for tsmc sucks.