+1 to always measuring. That said, we have done some experiments regarding power, including on Android, and it looks favorable.

The general rule of thumb is that a GPU has about 10x the raw throughput per joule as a CPU (which, today, is basically the same metric as throughput per dollar). So if your GPU is only barely faster than the CPU because of overheads of the parallel algorithm, you might not win, but if it sails way past the CPU because it's work efficient and lean (as I believe this work is), you do win both on power and throughput (frames per second).