THe theory is that the t-berd core XP1700 has a higher core limit clock speed than a palo XP1600 core. Therefore it should give you more room to overclock, since it seems to be a underclocked core.
I dont think most or your average Agoia will do 2 ghz on air, it seems like a bit of a exagration to me. It seems however most if not all (with good component) will hit between 1700 mhz to 1800 mhz, with exceptional ones (with high voltage) reaching 1800+ mhz.