Nor heat and power too ! I seem to recall AMD releasing a video mocking GTX 480 for exactly the same stuff 290X is doing !
Drawing nearly twice the power of the 5870 while performing 10% faster probably had something to do with that. The 290 is drawing what, 10% more power while performing the same. And it's cheaper as well!
The comparison isn't remotely valid. Also calling AMD's turbo half-baked is completely ridiculous. It's likely accounting for a large part of the performance gains and this will surely be seen with proper coolers.