2. GTX580's maximum overclock is around 900Mhz. How is it possible for a chip of the same architecture to have 875Mhz base clock? It's possible that shader-to-core clock ratio is reduced but then high clock doesn't tell anything about actual performance without knowing shader domain clock.
GTX 460 achieved high clocks because of the smaller die-size and because of the less tranzistor.
Combine this with the tweaked GF110 silicon and you will have even higher clocks.
And by the way GTX 570 have a 219W TDP and it's a huge chip, 529mm2.
Think a 350mm2 chip what TDP will have.
And probably the GTX 560 will have a higher voltage than GTX 460, but still almost same oc. headrom.
Still Nvidia is starting to equal Amd in Gpu frecuencys, GTX 560 might do this(only 6870 at 900Mhz will be higher), and we know, clock/clock Nvidia is a little faster.