I don't have access to the actual paper, but looking at the linked results[0]:
Core Name Performance (MIPS) Energy (J) Power (W)
Cortex A8 178 25 0.8
Cortex A9 625 11 1.5
Atom N450 978 16 2.5
i7-2700 6089 28 25.5
So A9 delivers 625/1.5 = 417 MIPS per Watt, whereas the i7 delivers 6089/25.5 = 239 MIPS per Watt and the Atom delivers 391 MIPS per Watt.
In addition, their spreadsheet has an "energy" tab calculated from a "normalized" power figure (where Atom comes out on top), but if you multiply the measured figures without the dubious adjustment, it seems that the A9 is actually more efficient (at least when you consider the board power), and MIPS is conspicuously absent from this spreadsheet. So the fundamental conclusion is "either ARM or Intel are better, but it depends on what you measure under what workload".
In addition, their spreadsheet has an "energy" tab calculated from a "normalized" power figure (where Atom comes out on top), but if you multiply the measured figures without the dubious adjustment, it seems that the A9 is actually more efficient (at least when you consider the board power), and MIPS is conspicuously absent from this spreadsheet. So the fundamental conclusion is "either ARM or Intel are better, but it depends on what you measure under what workload".
[0] http://research.cs.wisc.edu/vertical/wiki/index.php/Isa-powe...