No other CPU in the Nintendo CPU family has ever achieved clocks as high as a Expresso. The highest achieved with overclocks was 1.1 Ghz I belive and the performance increase is always small with a huge increase in heat production and power consumption. This is why it was always annoying when people insisted that the Wii was an overclocked Gamecube. The hardware doesn't overclock well at all.
We do no not know the entirety of the Espresso's design so to say it absolutely can't reach an overclock of x2 since is could very well be underclocked from all we know.
I've heard nothing of a GPU power increase.
The CPU would likely not be able to be clocked much higher... a rough guess would be 1.4GHz would be pushing the max you could see from the current design at 45nm. The main reason is the extremely short stages, there hasn't been anything clocked this high on such a short stage. Of course if Nintendo continues to use this family, they would find higher clocks as they push the processor to lower nodes, bringing it down to 20 or 16nm could yield a very large jump in clocks, still well short of the 3.5ghz that ridiculous rumor talked about but 2GHz to 2.5GHz is probably possible on smaller nodes though the stages would still be the largest obstacle.