It's annoying that the actual paper that article summarizes, the paper by "the team from the University of Wisconsin", does not seem to be available yet. Supposedly it is not yet published. Thanks to Google, not the author of the article, I've managed to track down the older version of the paper (the one without the A15 and without the Bobcat and Loongson), it is over here:
http://www.cs.wisc.edu/vertical/papers/2013/hpca13-isa-power-struggles.pdf
I really don't like it when people present things without giving a decent pointer to the source material.
According to
http://en.wikipedia.org/wiki/Comparison_of_ARMv7-A_cores, a Cortex-A15 performs 3.5 to 4 DMIPS/MHz (per core) while a Cortex-A8 does 2.0 and a Cortex-A9 does 2.5. This is for plain integer stuff, no floating point (where A15 should be much better).
So roughly, a 1GHz A8 should correspond with a 800MHz A9 and with a 500 to 570 MHz A15.
Obviously an A15 at 1.66 GHz consumes way more power than an A8 at 600MHz. I can't find any solid numbers, but according to the graph (Fig. 8) it would consume between 4 and 7 times more power (while doing about 5.5 times more work, or in the case of floating point stuff, about 9 times more work).
However, those are just two data points. On the Pandora we run the A8 at anything between 500 and 1200 MHz, and we have two different SoCs
with slightly different power characteristics. On the Pyra I would expect us to also have a broad range of clock speeds. For the A8 @65nm (like the ones in the CC and ReBirth units), 500MHz is pretty much the optimal point in terms of performance per energy: if you clock it higher, the extra consumption is larger than the extra performance; if you clock it lower, the improved consumption does not compensate for the loss in performance. So if you just need to get a task done (e.g. start a browser, render a page), your battery will lose the least amount of juice if you do it at 500MHz. For the A8 @45nm (like the one in the 1GHz units), the optimal point is around 600MHz but in the 1-1.2GHz range it also performs well.
So I'm interested at what the perf/W is of the A15 at other clockspeeds.