the wattage measured here is not just the processor, its also the entire boards.
Ive done some benchmarks testing Intel Atom processors Atom330's and D525's against Tegra3 processors. On average the Terga3 processors outperformed the Atoms 4x-8x in Flop/s per Watt.
Admittedly that is not the only important metric, but gives an initial performance comparison between ARM and x86 performance