Now, don't get me wrong, there are quite a few differences in the structure of these processors which will impact efficiency in different areas, so this shouldn't be taken as a straight comparison.
But it's interesting to see the drastic differences between the die size of the Cortex CPU vs the Intel variants and noting the transistor count. For example, a dual-core A9 has around half the transistors of an Atom 270, but 1/5 the size!
The size of the whole SoC brings the size of the die to parity with the early Atom CPU, though still far below that of the i7.
I wish I knew more about the architecture to make sense of what's going on. Could it be the ARM RISC instructions bringing down the size, a lack of features, or just better engineering? I wonder how ARM would look with similar features as an IA32 CPU.